The arc scale is graduated in dual ranges of 0-250x 1 gm and 0-1000x5gm which can be set using the weight arm provided.
This is the balance shaft from the New Haven wind up clock pictured below.
Often the case sticks around the starter motor, it helps to have a padded pliers handle to gently pop it loose.
Make soft bend out then soft bend in.
There are several books that explain this type of escapement.
I free hand the scratch as using straight edge can often offset.