This is the small rod which slide the weight over the graduation.

US Pharmacy scale

Made by
The Torsions Balance Co, New York

capacity 120 gram
Class A

Wooden case with wood / glass lid.

The black glass cover has two clear areas for
A = The indicator
B = A slider weight on a graduation
( 10 Gram and 15.4 grain ) 

This front wheel take the balance in and out of the weighing position.