How Do You Calculate Horizontal Angles in Surveying?

[ScieneBoy]

Homework Statement

I have been told to work out the Horizontal Angle when given the Horizontal reading of face left and face right at different sights. For example:

Face Left---------Face Right

A - 26 12 48--------206 12 59
C - 172 23 08--------352 23 17

I am unsure how to work out the Horizontal Angle from here. I know 172 - 26 = 146 is correct but when I attempt the likes of 8-48 = 40, it comes up wrong.

Any help on this please?

 

[mgb_phys]

You are supposed to subtract each face left from face right.
If you did it right you shoudl get the same answer for each set of measurements

 

[ScieneBoy]

As silly as this may sound, how would this be done on a calculator using the numbers given? Thanks so much.

 

[mgb_phys]

if you have a caluclator with a dms button use that, otherwise simply convert into decimal degrees and then convert back at the end.
eg. 26 12 48 = 26 + 12/60 + 48/(60*60) = 26.2133

Be carefull of readings where you go over 0/360. ie left =359, right=1 is a difference of 2