Name: OS Grid Reference DF
Author: simonletts

This data field is a reworked version of my simple data field OS Grid Reference app (https://apps.garmin.com/apps/d56ff2c7-98d6-4390-8e99-4c844f1f32d1)

The app 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 widget 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 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”.

The main driver for making this version was an attempt to optimise the font size and layout so 10 figure grid references can be displayed better, particularly in small data fields, i.e. when you show several data fields on one screen. Please note it's not possible for 10 figure references to fit into the smallest data fields on every device.

Differences from the original
1. Supported by fewer devices - it might not exist for yours.
2. Uses more memory, this is the reason for point 1.
3. Layout differs for some devices and some data fields.
Depending on your use, the original might be better for you.
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 definitely recommend you to have look at Chris's page.
The data field 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 data field on my vívoactive® HR and other devices in the simulator. Please contact me if you have any problems, comments or requests. In particular there is probably still more tweaking that could be done to the labels & font sizes; let me know if you would like me to customise a specific layout. Include your email address if you would like a reply.
The original can be found at https://apps.garmin.com/en-US/apps/d56ff2c7-98d6-4390-8e99-4c844f1f32d1
I've also made the app as a widget, available from https://apps.garmin.com/en-US/apps/10473162-3729-40e9-9a72-b7c16528c758
Disclaimer
Please note that I can accept no responsibility for the correctness of the grid references shown. You should never rely on this data field alone for navigation purposes. To be safe, always understand how to navigate without your Garmin device.