A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: John D. Howard
Date: 2016 Apr 7, 08:06 -0700
On some theodolites there is a cap on the horzontial axis that you can remove and shine a light onto the cross hairs.
A knob on top of the telescope moves a tiny flat paddle that works like a mirror to reflect light from the axis port to the cross hairs.
Without a manual it is hard to know for sure but worth a try.