Oertling model 5SBP analytical balance with separate telescope, serial no.11192, made 1910.

This is an early example of an arrangement for observing the final deflection of the balance by means of a reflected ray of light. A telescope is fixed to a vertical scale, which it can observe by reflection in a mirror placed on the beam of the balance (a prism suspended above the beam turns the optical path through the required right angle). The scale appears to move across the field of the telescope as the beam is deflected.