Grid references are simple to work out and follow a logical pattern, you simply start with the largest square and work your way in. On the larger scale the whole country is split into 100km by 100km equally sized squares, these are referred to by a combination of two letters. Virtually all of Suffolk falls into either the 100km grid squares of TM or TL indicated by the black lines on the map (see map 1) These larger 100km squares can then be broken down into 10km by 10km squares indicated on the map in dark blue. Each dark blue square is referred to with an additional 2 numbers representing its eastings co-ordinate (across the bottom) followed by its northings co-ordinate (up the side). So for example the red square on the map falls within the 100km square of TM and in the further 10km subdivision of 3 (eastings) and 4 (northings). This 10km square is therefore referred to as TM34.

Sometimes it is necessary to provide grid references at 6 or even 8-figure accuracy. If we look at the red 1km square of TM3747 in more detail (see map 2) we can break it down into 100m by 100m squares (these dashed lines do not actually exist on an OS map) and can record grid references at an even finer scale. For example, the bridge over the River Tang at Boyton can be worked out as TM37 (+ 6 further subdivisions) 47 (+ 5 further subdivisions) giving a 6-figure grid reference of TM376475. An 8-figure reference would break the 100m square into 10 by 10 m squares and so on.