How to Calculate Horizontal Distance between two points with Triangle method

In this video, I try to Explain, How to Calculate horizontal distance between two H Beams. For this purpose, I use my total station and get an angle  from Total station to 1st H beam top and other angles get from Total Station to other H beam top angle which value is 30 degree, So I make to triangles and

use Tan option (Perpendicular over Base)