Thread: How to calculate shooting angle?

You have three main ways of dealing with shooting at angles:
1. Inputting the angle into a ballistic solver. The most accurate.
2. Rifleman's Rule: line of sight (LOS) distance x Cosine (angle) = horizontal distance (HD)
Use HD for drop and LOS for wind. Tends to hit high.
3. Improved Rifleman's Rule: bullet drop x Cosine (angle) = corrected drop
Do not correct windage. Tends to hit low.

2 and 3 are approximations. Your rangefinder is using the Rifleman's Rule. I would recommended comparing different ranges and angles to see which combinations have an acceptable error.
For my applications (no more than 0.1mil of error) I found the following limits for the Rifleman's Rule:
5° good till 1500m (didn't check further)
10° 600m
15° 350m
20° 250m
>25° don't use it

You can calculate the angle from you rangefinder with:
angle = inverse cosine (HD/LOS)