4. Notes clarity

a. Zeroing BS readings

Because it's easy to do on a TSI, it's tempting to zero the horizontal angle reading on each BS sighting, Figure D-8.


Figure D-8
Resetting Angle


While this makes it easier to calculate the angle, it can be confusing to a third party. How were the measurements made?

As two complete D/R sets, or,

Two direct measurements first rotating back and forth between A and C, then two reverse measurements rotating back and forth between A and C?

Allowing the angle to accumulate without zeroing intermediate BS sightings makes it clear the order in which the measurements are made.

b. Mistake

Inevitably, a mistake is made, either reading the instrument, sighting, or incorrectly locking/unlocking the angle display. This will show in the notes as an angle with an excessive D/R difference. Figure D-9 shows a mistaken reading and how to correctly deal with it. 


The large difference for the second D/R set is an indication of a mistake.

Upon closer investigation, it looks like the mistake occurred on the second direct angle as the second reverse angle "fits" with the first D/R set.


The initial inclination is to toss the second direct angle and keep the second reverse angle.


However, accepting the reverse angle without a corresponding direct one doesn't compensate instrumental errors.

The correct way to address the mistake is to reject the entire second D/R set...


 .. and measure a third D/R set.


Figure D-9
Correcting An Angle Measurement Error