Japanese sighting device

[VPEP]

I just picked this up this weekend from a friend. I'm sure most people have seen these devices, but can anyone tell me its exact nomenclature and what and how it was used. Also, I paid my buddy $100 for it, because we couldn't find any currently for sale to gets price reference. Can anyone tell me what fair market value for one of these is so I can give him any difference if $100 was not enough. Thanks in advance,
Vic

[GeorgeP]

It is a goniometer -- measures angles. The case is dated to 1943, interesting case btw.


Tom

[VPEP]

Thanks very much for the information.