How do deep construction workers determine the depth of various construction projects?

Attention - stupid question ;-)).

The civil engineer will be on site soon. Now I generally have the following (probably funny for the experts) question:

The surveyor does the rough staking out and sets a height point (e.g. top edge of the finished floor).

How deep the hole "must" be we know from the basement builder (above-mentioned height point - thickness of the ground floor screed - thickness of the basement ceiling - room height - thickness of the base plate).

That part is clear to me. Now I just wonder, how does the civil engineer know how deep he is?

hm he measures? How else? Hehe :-)

That is clear to me ;-) But how does he do it. The highest point is quite a bit away from the pit, otherwise the [excavator] might roll over it. He somehow has to transfer the height of the point into the pit.

With these parts (weiß den Namen nicht) that stand on the tripod you look through. You place it on a known elevation point (for us a manhole) and the helper walks through the pit with a rod :)

With these parts (don't know the name) that stand on the tripod which you look through. You set it up on a known height point (for us a manhole) and the helper walks with a rod through the pit :)

Leveling instrument

Thank you, and me too ;-)