B&G WTP2 User manual

HB-0916-03
WTP2 User Manual
B&G Ltd.
Premier Way
Abbey Park
Romsey
SO51 9DH
UK
Tel: [phone]
Fax: [phone]
www.bandg.com
[email protected]

HB-0916-03

i
Certification
This equipment generates, uses, and can radiate radio frequency energy and, if not installed and used in accordance
with the instructions, may cause harmful interference to radio communications. However, there is no guarantee that
interference will not occur in a particular installation. If this equipment does cause harmful interference, the user is
encouraged to try to correct the interference by relocating the equipment or connecting the equipment to a different
circuit. Consult an authorised dealer or other qualified technician for additional help if these remedies do not correct
the problem.
The Wave Technology Processor 2 (WTP2) meets the requirements for CFR47 Part 15 of the FCC limits for Class B
equipment. WTP2 meets the standards set out in European Standard EN 60945: 1997 IEC 945: 1996 for maritime
navigation and radio communication equipment and systems.
Trademarks
All rights reserved. No part of this manual may be reproduced or transmitted in any form or by any means including
photocopying and recording, for any purpose without the express written permission of B&G.
Information in this document is subject to change without notice. B&G reserves the right to change or improve its
products and to make changes in the content without obligation to notify any person or organisation of such
changes.
B&G, Wave Technology Processor, WTP and WTP2 are all trademarks of Brookes & Gatehouse Ltd. and may not
be used without the express permission of Brookes and Gatehouse Ltd.

ii
Product Liability and Safety Warnings
Brookes and Gatehouse Limited accept no responsibility for the use and/or operation of this equipment. It is the
user’s responsibility to ensure that under all circumstances the equipment is used for the purposes for which it has
been designed.
Warning: Calibration
The safe operation of this equipment is dependent on accurate and correct calibration. Incorrect
calibration of this equipment may lead to false and inaccurate navigational readings placing the
yacht into danger.
Warning: Navigation Hazard
The WTP2 system is an Electronic Navigation aid and is designed to assist in the navigation of
your yacht. It is not designed to totally replace conventional navigation procedures and
precautions and all necessary precautions should be taken to ensure that the yacht is not placed
into danger.
Caution: Electrical Supply
This equipment is designed for use with a power supply source of 12V dc. The application of
any other power supply may result in permanent damage to the equipment and invalidating the
warranty.
Caution: Cleaning
The use of alcohol or solvent-based cleaners will damage this equipment and any warranty in
force will be invalidated.
Caution: Display Installation
Displays installed into locations manufactured from conductive materials (e.g. Steel, Carbon
Fibre etc.) should be insulated from the structure to prevent damage to the casings as a result of
the effects of electrolysis.

iii
Preface
This manual is in three parts:
Basic Operation
Chapter 1: is a brief introduction to the WTP2, outlining the way the unit works and some of the differences
with other instrument systems.
Chapter 2: contains information about the basic operation of the WTP2 in conjunction with the B&G Deckman
software.
Most users should be able to operate the WTP2 from Deckman using the information contained in this section.
Customisation
Chapter 3: outlines the way a PC can be used to upload or download files to or from the WTP2.
Chapter 4: contains information on the use of the data files; these allow you to control the input of variables
onto the system and the way these are sent back out to the displays.
Chapter 5: concerns the calibration, damping and settings options available.
These chapters are mainly aimed at more experienced users, who may wish to alter variable inputs and outputs.
Installation and Maintenance
Chapter 6: outlines the installation of a number of different components, and is therefore aimed primarily at
those involved with the initial installation of the system; general wiring information is also included
in this section.
This section is aimed mainly to assist with the installation or maintenance of the system.

iv

Contents
v
Contents
CHAPTER 1: INTRODUCTION TO THE WTP2 .......................................................................... 1.1
System Description ......................................................................................................................... 1.1
Sensors ........................................................................................................................................... 1.1
Typical Setup................................................................................................................................... 1.2
CHAPTER 2: BASIC OPERATION.............................................................................................. 2.1
WTP2 Menus Seen on the Full Function Displays (FFDs) ............................................................. 2.1
The Keys ......................................................................................................................................... 2.1
Examples of Operation.................................................................................................................... 2.3
Input Selection via Deckman........................................................................................................... 2.4
Deckman Control Facilities ............................................................................................................. 2.7
CHAPTER 3: USE OF A PC ...................................................................................................... 3.12
Introduction.................................................................................................................................... 3.12
Deckman ....................................................................................................................................... 3.12
FTP................................................................................................................................................ 3.13
Terminal ........................................................................................................................................ 3.14
CHAPTER 4: DATA FILES .......................................................................................................... 4.1
Defining the variables...................................................................................................................... 4.2
Input Configuration Files ................................................................................................................. 4.4
Display Output configuration files.................................................................................................... 4.9
Deckman Output configuration files ..............................................................................................4.15
Optional Files (Advanced)............................................................................................................. 4.21
Example on using the data files .................................................................................................... 4.24
User variables ............................................................................................................................... 4.25
CHAPTER 5: PARAMETERS ...................................................................................................... 5.1
Calibration ....................................................................................................................................... 5.1
Sensor Calibration........................................................................................................................... 5.4
Filtering and Damping ..................................................................................................................... 5.6
Sensor Damping.............................................................................................................................. 5.8
CHAPTER 6: INSTALLATION..................................................................................................... 6.1
Physical Installation......................................................................................................................... 6.1
Fastnet Network Installation ............................................................................................................ 6.1
Ethernet........................................................................................................................................... 6.3
NMEA .............................................................................................................................................. 6.4
Paddlewheels .................................................................................................................................. 6.4
GPS................................................................................................................................................. 6.4
Rate Gyros ...................................................................................................................................... 6.5
Depth............................................................................................................................................... 6.5

Contents
vi
WTP2 connector wiring ................................................................................................................... 6.6
CHAPTER 7: UPGRADING THE WTP2 ...................................................................................... 7.1
Upgrade Procedure ......................................................................................................................... 7.1
APPENDIX A: WTP2 VARIABLES............................................................................................... A-1
APPENDIX B: WTP2 DIRECTORY STRUCTURE....................................................................... B-1
APPENDIX C: SUPPORTED COMPASS TYPES ........................................................................ C-1
APPENDIX D: DIAGNOSTIC MESSAGES DISPLAYED VIA TERMINAL.................................. D-1
APPENDIX E: WIND CALCULATION FLOWCHART ..................................................................E-1

Chapter 1 Introduction to the WTP2
1.1
Chapter 1: Introduction to the WTP2
System Description
The B&G Wave Technology Processor in combination with the B&G Deckman software and range of H2000
displays make for the highest-level yacht racing instrument system in the world today.
Central to this high performance is the WTP2, a powerful processor running a Windows CE™ operating system and
a high speed analogue to digital board; such that calculations run some hundreds of times faster than on standard
instrument systems. This provides several benefits:
• All of the sensors can be sampled at higher data rates (100 times per second on analogue inputs)
• Wind calculations are improved by the addition of rate-gyro sensors to measure boat motion
• Compass inputs are enhanced using the same sensors
• Ethernet communications are used to allow high-speed communication with one or more PCs running the
Deckman tactical software
• The ability for users to create their own variables based on existing data
• Boat performance polars have a simple description and interpolation using cubic splines
• Additional terms are included to improve filtering and calibration (see Chapter 5:)
• Data is written to the display network at high rates (up to 10Hz)
• Users can configure the way information is displayed in menus with intelligent data switching.
Sensors
The WTP2 is designed to accept numerous different sensor types to allow the system designer to use the most
appropriate device in each application. All of the standard B&G H2000 sensors are compatible except that the
WTP2 uses an active NMEA sensor for Depth rather than the passive sensors normally used on H2000.
In addition to the normal sensors the WTP2 system also includes a 3-Axis Rate-Gyro sensor unit for measuring the
pitch, roll and yaw motion of the boat. It is this sensor that gives the WTP2 its name because it allows the removal
of the wave inertia components from the wind measured at the masthead.
If you have any sensor compatibility requirements that the standard WTP2 does not support please contact the B&G
Custom Projects team.

Chapter 1 Introduction to the WTP2
1.2
Typical Setup
The WTP2 is supplied with a straight through Ethernet patch cable that allows the WTP2 to be connected to an
onboard PC network via a hub or router.

Chapter 2 Basic Operation
2.1
Chapter 2: Basic Operation
The WTP2 is controlled from a PC running Deckman software, however basic control of the display of data around
the boat is carried our via the Full Function Display (FFD) units.
WTP2 Menus Seen on the Full Function Displays (FFDs)
When using the WTP2 all the information is contained in menus on the FFDs. The FFD simultaneously displays two
functions with accompanying descriptive text. Chapter 4: Data Files outlines how it is possible to customise these
menus and the data that is shown. This section simply describes how to navigate these menus and display the data
available.
The Keys
Keylock
To prevent accidental changing of the data displayed, two keylock features are available on the FFDs.
• Press the Enter and Lights keys simultaneously once. All keys except the Page key are locked.
• Press the Enter and Lights keys simultaneously once more. All keys are locked.
• Press the Enter and Lights keys simultaneously a third time. All keys are unlocked.
Lights Key
This key controls the level of illumination on the displays. One short press of the key provides full background
illumination on all system displays. Further short presses of the key decrease the illumination in three stages from
full brightness to OFF. The next press of the key enables full illumination again. This operation at any one FFD
invokes the same sequence on all displays connected to the system. However, display lighting can be localised so
that the level is adjustable for individual displays.
Caution
Do not press the Light key for longer than one second as this will switch the displays off. Should a
user inadvertently power off the displays it will be necessary to re-boot the WTP2 system to ensure
that all non-standard functions are displayed on the FFDs correctly.
Page Key
Operation of this single key enables the user to quickly access eight functions of the WTP2 System, by selecting any
one of the four pre-set page displays (2 functions per page) with a simple key press.
Default Pages:
• True Wind Angle / Opposite Tack
• True Wind Direction / Timer
• VMG to Waypoint / Cross Track Error
• Course Over Ground / Speed Over Ground

Chapter 2 Basic Operation
2.2
Notes
• If you are ‘lost’ in the system, press the Page Key to immediately return to the top-level display.
• The initial four pages can be reconfigured using the remaining keys and the menu system (see Page
Display Configuration below).
• Successive presses of the Page Key displays each page in rotation.
• Holding down the Page Key for 2 seconds initiates control of 20/20 and 40/40 displays.
Scroll Keys
Two scroll keys are provided, Scroll Up and Scroll Down, and are used to scroll through the menus.
When the Scroll Up Key is first pressed, the large digits in the upper display are no longer displayed and the name
of the current menu flashes in the upper text. If the key is held down, then the upper text will scroll through the top-
level menu choices. If, when you are scrolling up, the required menu choice is passed then pressing the Scroll Down
Key will allow you to return to the required choice. When the required menu choice is found, the text will flash until
selected by pressing the Enter Key.
Enter Key
The principle use of the Enter Key is to activate selections chosen from the menu by the scroll keys. As a general
rule, when any menu choice is flashing, pressing the Enter Key will select that choice.
Speed/Depth (SPD/DEP) Key
Pressing the SPD/DEP Key will select the Speed/Depth display. After selection of the Speed/Depth functions,
successive operations of the SPD/DEP Key will display the following information in a fixed order:
• Boat Speed / Depth
• Boat Speed / Speed Over Ground
• Boat Speed / Apparent Wind Angle
• Boat speed / True Wind Speed
Wind (WIND) Key
Pressing the Wind Key will select the Wind Display. After selection of the Wind Display, successive operations of
the Wind Key will display the following information in a fixed order:
• Apparent Wind Speed / Apparent Wind Angle
• True Wind Speed / True Wind Angle
• True Wind Speed / True Wind Direction
• Velocity Made Good / True Wind Angle
Navigation (NAV) Key
Pressing the NAV Key will select the Navigation Display. After selection of the Navigation Display, successive
operations of the NAV Key will display the following information in a fixed order:
• Heading / Course Over Ground
• Heading / Boat Speed
• Distance to Waypoint / Bearing to Waypoint
• Tide Set / Tide Rate

Chapter 2 Basic Operation
2.3
Examples of Operation
The general principle for operating the FFD will be made clear by the following examples of function and page
selection.
Function Selection
Our first example will be to select another function for one of the pages. The new function is True Wind Angle and
since we want to place this function in the bottom display we will be using the Scroll Down Key.
1. Press the SPD/DEP Key until the display is showing BOAT SPD in the upper display and DEPTH in the
lower display.
2. Press Scroll Down, the lower text now shows DEPTH flashing, the upper display is not affected.
3. Press Scroll Down until the lower text shows WIND flashing, the upper display is not affected.
4. Press Enter, the lower text now shows APP W/A flashing, the upper display is not affected.
5. Press Scroll Down until the lower text shows TRUE W/A.
6. Press Enter again, the lower display now shows required function, the upper display is not affected.
We are now able to view this function. If we press the Page Key, the configured pages will return and True Wind
Angle will no longer be displayed. If you wish to keep True Wind Angle on a page, then you can configure the page.
Page Display Configuration
The Page Key allows the user to configure four pages per FFD depending on the required use at that position.
To store the setting in the previous paragraph as a permanent new page, proceed as follows:
1. Repeatedly press the Page key until the desired page you wish to re-configure is shown.
2. Press Scroll Up or Scroll Down and until the display shows CNFG DSP.
3. Press Enter, PAGE is shown in the appropriate display.
4. Press Enter, the digital display is blanked and the two functions selected are displayed in the text.
Note at this point, either of the two functions may be changed if required using the Scroll Up or Scroll Down Keys
as per “Function Selection” above.
5. Press Enter to accept the new page configuration and restore the digital display.
You are able to configure each FFD on the boat individually to suit the needs of the crew in the immediate vicinity.
All page displays are held permanently in the display memory.
NAV Key Configuration
Our second example is configuring the NAV key. The NAV key allows the user to select either Rhumb Line or
Great Circle navigation information to be displayed; by default the FFDs show Rhumb Line pages. WTP2 only uses
Great Circle waypoint data so we need to modify this page. To select the Great Circle mode, proceed as follows:
1. Press the Page Key once.
2. Press Scroll Up until the upper display shows CNFG DSP flashing.

Chapter 2 Basic Operation
2.4
3. Press Enter, the upper text now shows PAGE flashing.
4. Press Scroll Up to select NAV MODE GC (Great Circle).
5. Press Enter to select your desired choice. The display will stop flashing and the NAV key will display data
in GC.
Lighting Control
The backlight level on system displays is controlled by the LIGHTS Key. Use of this key normally controls all the
FFDs simultaneously, however the level of illumination on a single FFD can be set to be controlled individually via
the menu choice - LIGHTING →LOCAL.
1. Press and hold SCROLL UP or SCROLL DOWN until LIGHTING appears in the text.
2. Press ENTER and use SCROLL UP or SCROLL DOWN until LOCAL appears in the text.
3. Press ENTER again and the original page display appears. The FFD is now in local mode.
The LIGHTS Key now controls this display only. This will enable you to use (for example) very low backlight
brightness at the chart table, whilst using a higher backlight level on deck.
To return displays to system lighting control:
1. Select LIGHTING.
2. Press ENTER and use SCROLL UP or SCROLL DOWN to select SYSTEM.
3. Press ENTER again, the original page display appears and the lighting has returned to system control.
The lighting brightness is still controlled by successive short presses of the lower right hand key on an FFD in the
normal way. Displays which have their lighting control set to LOCAL will not be affected by the lighting control
input of another display.
The display backlight colour may be altered between RED (default) and GREEN. This is adjusted via the menu
choice: LIGHTING →RED or GREEN
1. Press and hold the SCROLL UP or SCROLL DOWN key until LIGHTING appears in the text.
2. Press the ENTER key and use SCROLL UP or SCROLL DOWN to select either RED or GREEN.
3. Press ENTER again and the original page display appears. The FFD backlighting will now be configured to
your desired selection.
Input Selection via Deckman
Multiple Compass, Boat Speed and GPS Inputs
WTP2 is able to handle up to three compass inputs (as well as associated heel and trim values), two boat speed
inputs and two GPS inputs. This is useful for testing purposes, to compare different sensors, or as a backup.
Variables to handle data from all of these inputs exist on the system.
To select which input you wish to use in the calculations on the WTP2 use the Instrument Control option in
Deckman (see ‘Settings’ on page 2.9). Whichever input is selected is then copied into the SelHdg (88), SelHeel
(89), SelTrim (90), SelBoatSpd (91) or Selected GPS (multiple functions) variables, this is then used in the
calculations and output to Deckman and displays as required. This selection is shown below for each of the
selectable variables, in each case the standard variable number is shown in brackets.

Chapter 2 Basic Operation
2.5
Heading selection
Heading1
(13)
Selected COG
(28)
Selected Heading
(88)
1
2
3
4
Heading2
(80)
Heading3
(83)
Heel selection
Heel1
(0)
Heel2
(81)
Heel3
(84)
Selected Heel
(89)
1
2
3
Trim selection
Trim1
(57)
Trim2
(82)
Trim3
(85)
Selected Trim
(90)
1
2
3

Chapter 2 Basic Operation
2.6
Boat Speed selection
Port_vs
(63)
Starboard_vs
(64)
vs2pad
(87)
Boatspeed
(2)
Selected SOG
(27)
Boatspeed2
(86)
Selected Boatspeed
(91)
1
2
3
For boat speed there are a couple of extra steps to take account of the damping and the fact that there may be
separate port and starboard paddlewheels.
The raw data from the standard port and starboard paddle inputs (63 and 64 respectively) are combined to make
Boatspeed, the WTP2 uses Heel Angle to determine which of the two inputs to use. The raw data from the second
speed sensor is used to make Boatspeed2 (Note that this stage is necessary in order to filter the raw data from the
sensors). Then, if you enter a 1 in sel_speed in the Settings dialog (see ‘Settings’ on page 2.9) then Boatspeed (2)
will be copied into SelBoatSpd (91), if you enter a 2 in the dialog then Boatspeed2 (87) will be copied and if you
enter a 3 SelSOG (27) will be copied.
By default WTP2 is setup to look at Boatspeed (2).
GPS Selection
GPS 1
COG1 (100)
SOG1 (101)
QHD1 (102)
SVA1 (103)
UTC1 (104)
1
2
GPS 2
COG2 (105)
SOG2 (106)
QHD2 (107)
SVA2 (108)
UTC2 (109)
Selected GPS
selCOG (28)
selSOG (27)
selQHD (79)
selSVA (78)
selUTC (77)

Chapter 2 Basic Operation
2.7
Deckman Control Facilities
To access the WTP2 control facilities in Deckman, choose gmenu →instrument control. You will then see a
dialog on the screen. Each box along the top of the dialog accesses a different control facility, as described below.
Output
Controls the output of Deckman variables to the WTP2 to be viewed
on the displays.
In addition to the standard WTP2 system variables it is possible to output up
to nine variables from Deckman to the WTP2 for transmission to displays.
As supplied WTP2 declares a Deckman menu containing four functions
(remote 1, remote 2…), if more than four Deckman variables are required
additional menu items will need to be added to the usermenu.d file (see
page 4.12).
To output a variable, click on the first blank line of the variables column,
select the appropriate Deckman variable from the list followed by OK. The
variable will be displayed on that line, with the channel column showing –1
and the current data shown in the final column. The –1 indicates that output
of this variable is currently disabled. To enable the output click on the
channel number (currently -1) and assign a channel number of either 1,2,3 or
4 (on the standard configuration). If the same channel number is assigned to
more than one variable then the data will oscillate between those variables
on the displays.
Damping
Allows you to alter the damping values on the WTP2. The values are
read from the WTP2 and any changes you make are sent as soon as
they are entered.
Each of the menu options has a number: this is the damping applied to that
instrument data. Generally, because the WTP2 uses a much faster processor
and more sophisticated calculations, you will be able to use much lower
damping values than with conventional systems, between 0.5 and 5 is
suggested for normal variables.
Note: You can modify which variables are listed in this dialogue using the
data files. See ‘damping.d’ on page 4.19

Chapter 2 Basic Operation
2.8
Calibration
Controls the calibration of variables by allowing you to input a
calibration value to a particular variable:
Bspd_port and Bspd_stbd are boat speed calibrations for the port and
starboard side respectively in Hertz/knot. If you have only one boat speed
sensor enter the same value in both port and starboard. If you do not know
what these values are, the boat speed can be calibrated using the cal
boatspeed option, see page 2.11.
Heading1 is the offset value for compass 1. Once you have run the
AutoSwing facility on the Halcyon compass (or the normal routines for other
types of compass sensor), you still need to align the unit in the boat
correctly. The most accurate way to do this is to sail on a known bearing
towards a fixed charted object a long distance away. You then use Heading1
to correct the compass bearing on the instruments until it matches the known
bearing of the object. A positive offset will increase the reading of the
compass heading.
heel1 is the offset value for the first heel sensor. If the heel angle does not
read zero when the boat is sitting upright in the water it is necessary to enter
a correction value here. The heel sensor shows positive values when you are
heeled to port, as on starboard tack upwind.
trim1 is the offset value for the first trim sensor. If the trim angle does not
read zero when the boat is sitting upright in the water it is necessary to enter
a correction value here. The trim sensor shows positive values when the bow
is trimmed down.
MHU_angle is the offset angle for the masthead unit sensor at the top of the
mast. If you enter a positive value, it will decrease the Apparent Wind Angle
on starboard tack, and increase the Apparent Wind Angle on port tack.
forestay is for the calibration of a forestay loadcell fitting. Wind up the
runner or backstay to a known value of tension (perhaps by reading it from
the loadcell value if already fitted and calibrated), and then enter this value
in the forestay box. Check also that the reading is 0 when there is no load on
the forestay.
depth is the offset for adjusting the depth sensor reading from the transducer
position to either the keel (negative values) or the waterline (positive values).
Note: You can control which variables you are able to calibrate from this
dialogue by adjusting the ‘svcals.d’ data file. Please see on page 4.18.

Chapter 2 Basic Operation
2.9
Settings
The settings dialogue controls all the normal items required to setup
the WTP2.
mast_height is used for wind calculations involving the rate gyros. This
should be set to the distance from the waterline to the masthead sensor in
feet.
leeway_cal is the leeway calibration value. A value between 8 and 13 is
usually appropriate for most modern boats.
use_heel should be set to 1 if you have a heel sensor and 0if you do not.
A heel sensor is highly recommended to achieve accurate wind data.
use_gyro determines whether or not the system uses data from the rate
gyro sensors to correct wind calculations. 1=use gyro data, 0=do not use
gyro data. Normally there is no reason to disable this function.
variation is magnetic variation. This is calculated automatically using
data from the GPS. If the GPS is not providing this information it can be
entered here. It will be overwritten by GPS information if it becomes
available. Enter a positive value for East variation, negative for West.
Osc_time,UP-RE_angle and RE-DW_angle all refer to the switching of
variables on displays according to either point of sailing or over time if
this is specified in userout.d (see Chapter 4: Data Files for more
information). The osc_time is the frequency with which the displays
alternate between showing different variables, units here are 1/10th second;
UP-RE_angle is the angle for the change between upwind and reaching
settings; RE-DW_angle is the angle for the change between reaching and
downwind settings.
TWS_factor will reduce or adjust wind speed by multiplying by this
factor; this is used as an adjustment for wind weight.
use_mrot allows the option of using data from a mast rotation sensor.
Available settings are 0 (off), 1 (on, using absolute value) or 2 (on, using
+/- for fully rotating masts).
use_3D provides the option of using (1) or not using (0) Gyro Heading
(compass heading adjusted for rate gyro inputs) when calculating wind
information. It is important that this is set to off (0) if the compass input
you are using is already rate-gyro corrected.
damp_3D should not be changed under normal use (0.970 is the default
value).
sel_comp, sel_heel and sel_trim control which input is used for heading,
heel and trim respectively. Refer to ‘Multiple Compass, Boat Speed and
GPS Inputs’ on page 2.4 for more information.
sel_speed controls which input is used for boat speed. Refer to ‘Multiple
Compass, Boat Speed and GPS Inputs’ on page 2.4 for more information.
sel_GPS controls which set of GPS data is used for position, SOG, COG
etc. Refer to ‘Multiple Compass, Boat Speed and GPS Inputs’ on page 2.4
for more information.
boatlog this allows you to reset the Log variable to any value you wish
(though zero is likely to be most useful).

Chapter 2 Basic Operation
2.10
Bounds Checking
To prevent errors caused through the loss of characters between the
instrument system and the PC WTP2 allows the user to set limits on
input values.
The incoming data is checked against the previous values. This display
allows you to change the bounds that are used for each incoming variable;
smaller values make errors less likely but increase the possibility that the
numbers will ‘stick’ because of dramatic boat manoeuvres.
The values shown in the example should be used unless you are experiencing
difficulties with a particular variable.
Reset Bounds Checking
Clicking this button will cause the next set of incoming data to
overwrite the old, even if it falls outside the error bounds. This is not
normally required but may be necessary under some circumstances.