Plumb Bobs have always been a necessary tool to make sure things are installed perfectly vertical. Can you imagine building a say 40 story tall building and keeping it perfectly vertical from bottom to top? say you were off 1/16" from one story to the next. In 40 stories that would mean 40X 1/16"= 2.5".
By hanging a plumb bob in a bucket of oil up the elevator shaft,on a piano wire and using it to measure off of on every story, you will be exactly on point as you build upward.
This might be the type of “Bob” that can be used for that.
Carpenters usually carried the classic Brass Plumbs in their nail belts for a quick handy way to set things vertical. Bubble levels are in use a lot, but they can get get damaged easily and not be accurate. A plumb bob is always right on.
Over the years there have been some novelty ones such as the “Barbie”