NavList:

Surely you understand that any competent machinist can remake the simple clamp piece.  If someone needs to know what that looks like, I can photograph and measure the clamp piece on mine.  The two devices are extremely similar.  The only difference I can see is that my device has the full circle and a second index arm.  In all other regards they are visually the same.   

All of the adjusting mechanism is there.  The index mirror is there.  The scopes are there, as well as the right angle eyepiece.  I cannot see the prism.  If that isn't there, then I agree it's useless.

In any device over 100 years old, you naturally want to be careful.  Check with the seller to insure it has the pridm.  If you want the device for an use and it must have all its original parts, then this isn't the one for you.  If it's for a sextant collection, these are rare as hen's teeth and you may want to consider it. The only other one of these I know of is in the Smithsonian, and that one is missing major parts.  If you are buying it for use, and a replacement clamp piece does not bother you, then I stick by my assessment.

Brad