You don’t, though; you can do it with math. Trigonometry is pretty useful in orienteering.
A quick and dirty method is to have something with a known height next to it and step back until the known object is the relative size of one thumb section, then count the number of thumb sections tall the unknown object is.
You do need to climb a mountain to know how tall it is.
If you haven’t, don’t tell people it’s 49.3 meters.
You don’t, though; you can do it with math. Trigonometry is pretty useful in orienteering.
A quick and dirty method is to have something with a known height next to it and step back until the known object is the relative size of one thumb section, then count the number of thumb sections tall the unknown object is.
And that’s great if you can document and explain how you got those numbers. That’s the point. You can’t just say it, you have to show your work.