NavList:

Brad, you wrote:
"Does this mean the requirements changed over time?"

As I mentioned before, I think this is very likely --even inevitable. For example, requirements for micrometer function would have been added sometime in the 1920s.

We've got a contemporary source in 1905 saying that "class A" requires (among other things!) an arc error no greater than 1', and another contemporary source in 1948 saying that "class A" allows no greater than 40" arc error. Those both strike me as very reasonable numbers for those eras. For an instrument-rating agency like Kew (and its successors), I would not expect changes in standards (at least in this kind of technology) more frequently than once in 25 years. I would be surprised if there was any standard "between" these two. Also sextant certificates did not really take off until the 1890s, so that 1905 standard is probably the original.

-FER
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