Unusually, it has a Rosewood Stem with sliding brass furniture and steel pins.

The guiding head is solid brass and has a lock nut which secure the selected measurement in place. 

The reverse spine has a rule scale in inches with 1/16th inch graduations.

One side of the stem has been stamped: W. R. Brenton whom I presume was the owner rather than the maker.

I'm sure there must be a patent somewhere to determine who made this fabulous item.

It measures 9 1/8" in length.