Titan TTS2 Manual page 66

6) Aim at the known point 1, press [F3](Angle) or [F4](Dist).
Press [F4](Dist) for example;
7) Start measuring;
8) Enter the input interface of point 2 ;
9) According to step 5)~step 8), when using [Dist] to measure,
the residual will be calculated.
10) Press [F1] to measure other known points, which are at most
five points;
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