Name: OS Grid Reference
Author: simonletts

This device app is the equivalent of my OS Grid Reference widget (https://apps.garmin.com/en-US/apps/10473162-3729-40e9-9a72-b7c16528c758.) It calculates and shows the Great Britain or Ireland Ordnance Survey grid reference for the current position.

It takes the latitude and longitude from your device's GPS location and converts it to the equivalent OS grid reference. This is displayed in the standard letters and digits format.

The GB Ordnance Survey National Grid is designed to cover Great Britain and its islands and the Ordnance Survey of Ireland National Grid covers the island of Ireland. If you are not inside either of those areas the app will show "Outside Grid".

The required number of digits can be chosen as a setting using Garmin Express or Connect Mobile. You can choose 4, 6, 8 or 10. The default shows six-figure (100m precision) grid references. You can also choose the all-numeric format of 12 or 13 digits which is 1m precision.

You can choose how the grid is selected and the default grid. The two National Grids overlap, i.e. there are places that can produce both a valid Irish & UK grid reference. If you choose “Best Guess” the app will decide which grid is most suitable. If you choose “Strict” the app will try with the default grid and if that does not produce a grid reference it will try the other one. This means you could get Irish references for some parts of Great Britain and vice versa. For areas that are only covered by one grid a reference will always be displayed using the appropriate National Grid. The defaults are “Best Guess” and “Britain”.

You can also choose whether to display the grid reference over 1, 2 or 3 lines. The 2 & 3 line layouts generally allow a larger font to be used for the numbers - useful for old eyes!

The display also shows the current GPS quality as seen by the device. This is indicated as None, Poor, Usable or Good. Pressing Menu will stop the app updating and fix the displayed grid reference.

The conversion routines are a cut down version of the excellent work at https://www.movable-type.co.uk/scripts/latlong-os-gridref.html (© 2002-2016 Chris Veness). The original scripts, and therefore this work, are released under an MIT licence (https://opensource.org/licenses/MIT), without any warranty express or implied. If you're interested in how it all works I recommend you to have look at Chris's page.

The app was created for my personal use – but I've shared it for anyone who would like to try it.

The icon was made by Pixel Buddha from flaticon (https://www.flaticon.com/authors/pixel-buddha) licensed by CC BY 3.0 (https://creativecommons.org/licenses/by/3.0).

I've tested the app on my vívoactive® HR and other devices in the simulator. Please contact me if you have any problems, comments or requests. Include your email address if you would like a reply.

I have also made the app as a simple data field, you can find it at https://apps.garmin.com/en-US/apps/d56ff2c7-98d6-4390-8e99-4c844f1f32d1

Alternatively you can download it as a complex data field app. This works in exactly the same way as the simple data field but the font size and layout is slightly different, mainly with small data fields. You can find it at https://apps.garmin.com/en-US/apps/3b19825b-2021-44e2-81f7-62c87877a456

Disclaimer
Please note that I can accept no responsibility for the correctness of the grid references shown. You should never rely on this app alone for navigation purposes. To be safe, always understand how to navigate without your Garmin device.