<P> In the Universal Transverse Mercator (UTM) system, grid reference is given by three numbers: zone, easting and northing . In the UTM system, the earth is divided into 60 zones . Northing values are given by the metres north, or south (in the southern hemisphere) of the equator . Easting values are established as the distance from the central meridian of a zone . The central meridian is arbitrarily set at 500,000 metres, to avoid negative numbers . A position 100 kilometres west of a central meridian would have an easting of 400,000 metres . Due to its popularity, and worldwide cover, the UTM system is used worldwide by NATO as well as many countries, including Australia and the USA . </P> <P> In the United Kingdom, a proprietary grid system is used . In Ordnance Survey maps, each Easting and Northing grid line is given a two - digit code, based on the British national grid reference system with origin point just off the southwest coast of the United Kingdom . Since the Eastings and Northings are one kilometre apart, a combination of a Northing and an Easting will give a four - digit grid reference describing a one - kilometre square on the ground . The convention is the grid reference numbers call out the lower - left corner of the desired square . In the example map below, the town Little Plumpton lies in the square 6901, even though the writing which labels the town is in 6802 and 6902, most of the buildings (the orange boxed symbols) are in square 6901 . </P> <P> The more digits added to a grid reference, the more precise the reference becomes . To locate a specific building in Little Plumpton, a further two digits are added to the four - digit reference to create a six - digit reference . The extra two digits describe a position within the 1 - kilometre square . Imagine (or draw or superimpose a Romer) a further 10x10 grid within the current grid square . Any of the 100 squares in the superimposed 10 × 10 grid can be accurately described using a digit from 0 to 9 (with 0 0 being the bottom left square and 9 9 being the top right square). </P> <P> For the church in Little Plumpton, this gives the digits 6 and 7 (6 on the left to right axis (Eastings) and 7 on the bottom to top axis (Northings). These are added to the four - figure grid reference after the two digits describing the same coordinate axis, and thus our six - figure grid reference for the church becomes 696017 . This reference describes a 100 - metre by 100 - metre square, and not a single point, but this precision is usually sufficient for navigation purposes . The symbols on the map are not precise in any case, for example the church in the example above would be approximately 100x200 metres if the symbol was to scale, so in fact, the middle of the black square represents the map position of the real church, independently of the actual size of the church . </P>

How accurate is a 8 figure grid reference