in the circle being graduated upon the lines of the small square shown in fig. 20. With such a diagram the bearings can be used as they stand, without reduction, and the signs + can be taken from the diagram itself.

and

FIG. 21.-Circular Diagram giving Values and Signs of Co-ordinates.

To illustrate the working out of co-ordinates, they are here calculated for the station points of the survey shown in Plate I, first by logarithms and then by traverse tables. The advantage of the latter is very apparent. The bearings and distances are taken from the field notes.

Example of Calculation of Co-ordinates from Field Notes (Plate I).

* One opening of the tables only as compared with five by the logarithmic method -a saving of 80 per cent. in time.

413·996
565.838

Diff. Dep.
Add from B

979 834

C