Beam Trammels/Caliper Iron CA 1880's

Offering this early design of a combination compass, dividers, inside and outside caliper in useable condition.  We have not seen one similar to this one in many years.  In fact, we have never had one just like it for sale in the past 20 years!  It might be a prototype, or a machinist may have made it, or, it may have been a production tool?  It really is a nice design, very flexible, made for larger parts measuring as the beam measures 18" long and the adjustable compass/dividers arms are 9.6" long.  The compass/dividers arms can be set square to the beam or set at an angle to the beam, whichever you prefer.  As far as we can tell there are no missing parts and this tool is fully functional.  As you can see there is a evenly spread pitting on the entire metal surfaces, not rusty now.  The pitting appears to be more of a casting process pitting, but it may have been from rust.   The knurled threaded nuts as you can see have been tighten will pliers over the years, some signs of wear on the knurl for this reason mainly.  I did need to use padded jaw pliers myself to tighten the nuts during testing.  So that they will hold if pressure was applied to the extreme ends of the arms.  A very rare tool to find intact!