Whenever I see an explanation of an old technology, I don't wonder "How do that work" but rather "How did they even build this"

How did they make vacuum and be sure it was indeed a vacuum ?

How did they melted that metal alloy into the right shape ?

How did they built those precise mirrors ?

How many times did they fail before succeeding ?

How did they lubricate and seal properly all components ?

I know I could explain 80% of those inventions easily by studying them for a few days each. I know I would never be able to build 1% of those machines myself, I'd constantly run into technical issues and it'd take me years for each