Inclinometer < cosine indicator < rangefinder with slant range function
Ranking is based on speed and ease of use
If all you have is angle, you need a calculator (or table or slide rule) to figure out its cosine, Then you have to multiply the slant range by the cosine to get the horizontal range.
A cosine indicator cuts one step. You just multiply the cosine by the slant range to get horizontal range.
The rangefinder cuts out both steps. You range while the slant range function is on and you get the horizontal range.