Find the location you want to calculate the northing for. The location will be in a grid box marked with two letters and one number. Ignore the letters. The number gives the beginnings of both the northing and the easting.
Suppose the location you are interested in was in the grid box marked AB 4567. The northing will begin with 45 and the easting will begin with 67. The surveyor's map will contain a list or table of prominent features and each of these will have a code. This code will supply the rest of the northing.
Suppose the code for a location of interest was AB 123456. This feature is in grid box AB, and the number 123456 is part of both the northing and the easting. In this example, 123 is part of the northing, and 456 is part of the Easting.
Combining the results from steps 2 and 3, we have 45123 as the northing. This should be a six-digit number. The fact that we have a five-digit number means that the units are 10 meters. Therefore 451230, or 451235, would be more accurate estimates for the distance to the equator. If the calculation produces a four-digit number, it means that the units were 100 meters. So the four-digit number 5678 would really represent 567800, or 567850 meters.
