NavList:

Fred, you write

<<Bill Morris' comment that the post-war lattice type frames had vernier 
adjustments is not in accord with my data.  That doesn't mean he's wrong and 
the inference from my data is correct>>

I don't think I said this. What I said was:

All Hughes and Son micrometer sextants had the same arc radius of about 160 mm, dictated by the 18 turns per inch pitch of the micrometer worm. Their late vernier sextants had a slightly larger radius, measured at the feather edge of the vernier, of about 170 mm. Practically all of Hughes' micrometer sextants were of the three ring pattern - with the exception of those blue-grey-painted ones made for the Admiralty and bearing a National Physical Laboratory calibration certificate rather than an "in-house" one. Though in the 1957 edition of  AJ Hughes' "The Book of the Sextant" he illustrates a micrometer sextant with a curve bar pattern frame, I have never seen one.  My understanding of the "Mate" was that they simply had larger errors on calibration than the "Master" which was also of three circle pattern.

Thank you for posting your data base of Hughes and Son sextants.

Bill Morris

Pukenui

New Zealand