I have been retired since 1999, but there were Keving Hughes, and Tamaya sextants as well as Plaths in those days. There were no plastic ship sextants, and I don't know anyone that would have had the guts to bring it out on the Bridge of any ship I was on.

All were good sextants. Generally a good sextant had a metal frame to preserve the adjustment integrity. That being said however, it was pretty common to check the error on the horizon or a star frequently.

I don't remember anyone claiming a half mile accuracy with a sextant fix. On a deep sea plotting sheet a pencil line would be a half mile wide in less than 40 degree latitude.

Most Second Mates in the days of celestial nav used HO 249 for Selected stars, and some used it for the Sun. 249 stars calculated Alt and bearing for 6 stars and marked three of them as selected. These stars were approximately 120 degrees apart and at a reasonable altitude. The Navigator often took two rounds of these three stars and then plotted three. If the fix was good he stopped, if he was concerned or the Captain grumbled he would add a fourth to prove the fix. The idea of the 120 degree spread was to eliminate the personal or other errors, as the fix would remain in the center if the error was constant. Don't forget to apply the precession/nutation correction to the fix. It can be a couple of miles at times. The same for the corrections for Polaris.

If you are faced with nothing but celestial nav and not sure of yourself do what the sailing ship Masters did when Longitude was such a problem. Set your course well to the East or West of the destination. That way you know which way to turn when you reach the latitude of your destination.

I used a Kevin Hughes for years, and later a Plath. The Plath was the top of the line in those days. On a boat I would only use a plastic sextant as a backup in case the "real" sextant got damaged somehow.

Godspeed