War Diary - Map Coordinates

Looking at the pages of the war diary of 179 Tunnelling Company, a number of map coordinates are recorded e.g. on the following page an MG (machine gun) dugout is mentioned on Sheet 57D, J.15.d.2.1 :

The National Libray of Scotland has a collection of WW1 British maps online. The sheet linked to the war diary page can be seen at :

Sheet 57D

The J square on the map covers the land near the villages of Bus-les-Artois and Coigneux.

The J square has 36 smaller squares labelled 1 to 36. We need number 15 ie the J.15 part of the coordinate.

Square 15 has 4 sub squares. A is top left, B is top right, C is bottom left and D is bottom right. We need the bottom right, and this gives us J.15.d in the coordinates.

Running along the bottom line running left to right (West to East) are 10 marks (Eastings). Going 2 marks in from the left gives us J.15d.2 for the coordinate.

Running along the right hand vertical line from bottom to top (South the North) are 10 marks (Northings). Going 1 up gives us the final part of the coordinate J.15d.2.1. 

Putting a rough mark on the map gives us :

The coordinate can be put in a tool called tmapper in the format 57d.J.15.d.2.1 to see the map against the current location.

and this can be used to help look at maps such as Google Maps to get an idea of modern location and to zoom in/out etc.