system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How are the heights of mountains measured?

Before people had satellites and electronic methods.
gpt
It's called surveying. You stand in a spot, measure the angle of inclination when looking at the top of the mountain, the angle of decline looking at the base, and know the distance from it. Using trigonometry, you can calculate the approximate height. If you are far enough away you can use the curvature of the Earth when you cannot see the base (for explorers sighting things in the distance).