A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: David Pike
Date: 2017 Jun 16, 09:20 -0700
Don’t know the difference. They have the mechanical averager drum sticking out from the bottom.
The M stands for magnifier, for easier star shots, Instead of the single fixed eyepiece, the M models had a two eyepieces on a bar which could be pulled out slightly against a spring and rotated through 180 degrees to change from what I believe was x1 to x2 magnification. DaveP