Portable, Hand Held Instrument - Purpose?

This black, metal cylinder came with a worn leather case. One end is a pinpoint and the other, open glass. I wasn't able to get a good picture of the view, but what you see when looking though the pinpoint end is a framed semicircle of light. On one side of this 6 inch tube is a lozenge shaped piece of glass that reminds me of a level. A number has been scratched on it, which makes me think it was owned by a company or the military. I bought it because it was interesting. I don't know how to search for its purpose. Can you help, please.

 

Try searching for "Hand Sight Level". They were / are used for rough leveling, and distance estimating.

 

Perfect. Thank you very much. I’ll go a searching.

 

Terrific answer. I found one like mine 1930's. I am pleased. Thank you.

Vintage Surveyor's hand held spotting level | eBay

 

Thank you @Erstwhile! I explored further and discovered the stamp on mine (extremely worn) that says Dietzgen Made in USA.