NavList:

Dear Frank

Thanks for your interesting study.

I especially liked the micrometer test, obviously it takes some patience but I wonder how real sextants perform on the same test. I would expect that rotating the drum any number of turns agrees with the arc engravings to the nearest degree winding it across the whole arc forwards and back, but is that really true? Away from my home and boat I don't have a sextant to hand to check.

Many of the faults you report would have cost no more if they did them correctly, except a bit of thought and care, but I wonder how easily one can machine an accurately pitched thread on the arc of a sextant?

As many have said before the driver is presumably a regulatory requirement to carry a sextant in some flag states that is weakly enforced. One imagines an inspector picking it up, weighing it in their hands and reading the label 'sextant' and ticking their list. I have seen adverts for marine HF radios on Alibaba that I don't believe exist and thought they might be for the same reason. Lets hope it does not extend to fake fire extinguishers or lifeboats!

Bill