In article ,
"R.H." wrote:

http://puzzlephotos.blogspot.com/

I actually have a #303... Saw it at a tool swap meet a while back, and
was playing with it. Asked the owner what it was. Said he hadn't a clue,
but it was mine for 50 cents.

I suspect it's some sort of survey equipment. Know for sure it was a
good bit over 50 cents new.

Erik