Grid references are truncated, and not rounded. The requirement to truncate is clearly defined in the margin notes of almost every topographical map, but there is frequent confusion about this. An Australian adventurous activity training organisation even had this wrong in its navigation training materials. The incorrect application of rounding may stem from modern use of calculators, computers and GPS devices for which rounding is automatic.
Why is this important? As an example of the possible significance of incorrectly applying rounding, review the figure at right. You are at the bullseye and need assistance. The correct 4-figure grid reference is 23 64 (4-figure GR used for clarity but same principle applies to 6- and 8-figures GRs.)
The bullseye is nearer the upper right of this grid square, so if rounding is applied, the GR would be incorrectly reported as 24 65. A search party would begin in the shaded square, most probably at the hut, wasting valuable time and potentially endangering lives.
Bearing and Distance
When entering the bearing to the next waypoint, the value should be the initial bearing to follow from the start point, which if following a track or contour may be different to the straight line bearing to the next point.
The distance value is the route distance to the next point, not the straight-line distance.
To estimate height changes, count the contour intercepts up and down along the proposed route, and multiply each total by the contour interval.
In the diagram above, the route ascends one contour interval, and descends five and a half. For a contour interval of 20m, the height gain is 20m and the height loss is 110m. Since time calculations are applied independently to climbs and descents, do not just use the elevation difference between the start and end points as an overall height loss of 90m.