The unit is a pantograph. By placing the "adjusting" connectors in the proper positions stamped on the unit (or reading the destructions) the unit can be used to either 1) enlarge or 2) reduce the size of an original "pattern". Depending which point of unit contains the trace point (follower) and which point contains the pencil point, the result will either be a reduced or enlarged resulting new "pattern". Of course today, we just scan the original, insert into our handy dandy cad software, and plot it to the scale needed as a "government job" at work. Ah yes, remember doing it the hard way with one of these units in the 50's and 60's !!!!!!!!