Help needed to Identify the use of this measuring device

[Hubcap55]

I was cleaning out my fathers house (3rd generation surveyor), and found this measuring tool of some sort. I can only assume it was used for surveying purposes but not sure. The name on it appears to be an old survey equipment company. Any help in identifying this would be greatly appreciated.

[Hubcap55]

Additional pictures

[hellsangle]

Fascinating! You might wish to contact Bud's son, Russ at the link below . . .

http://compleatsurveyor.com/WhatsNew/WhatsNew.html

I did a Google search and this is what I found . . .
Frese logo seems to have survey-roots to it?!

[Scott]

It looks a little like a chain tension gauge, except no spring.

It also looks a little like a thermometer for the chain, but no vial of mercury.

[Hubcap55]

A chain tension gauge makes a lot of sense. I’ll look into that. Thank you for your thoughts.

[Dave Lindell]

I would guess it's a hole depth kind of gauge.
Note that the farther the unhooked end gets away from the ruled base the higher the number.
And a vernier! That's some precise measuring.

[Scott]

Yeah I saw the vernier.

I have not seen a chain tension gauge with a vernier. You would have to have one guy just to stand there and read the vernier