ELI5 Everest - how did they measure it without GPS?

How did people measure the height of mountains in the past? Why are K2 and Annapurna considered more difficult to climb than Everest? Why is there debate about who was the first person to summit it? Who was the first woman to climb Everest? ... We explain like i'm five! Thanks to our sponsor Goodnight Stories for Rebel Girls - a fairytale podcast for kids about extraordinary women from all over the world. https://www.rebelgirls.com   Thank you to the r/explainlikeimfive community as always and in particular the following users whose questions and comments formed the basis of this discussion: kouhoutek, moonkeyman120, eamisagomey, moodoperator, msmelxx, axenhalligan, kelkulus, foragerr, itrandall & cynic_male Great Trigonometrical Survey Wikipedia: https://en.wikipedia.org/wiki/Great_Trigonometrical_Survey To the ELI5 community that has supported us so far, thanks for all your feedback and comments. Send us an e-mail: [email protected]