NavList:

Brad,
In the past like you I have advocated always approaching from the same side when using a micrometer sextant, but if adequately spring-loaded, it does not seem to matter to any detectable extent. Most micrometer mechanisms spring-load the worm against the rack (radial load) and the end of the worm against a solid abutment(axial load). Some do not have axial pre-load and rely on accurate fitting, e.g. some pre-WWII Hughes and Son, Filotechnica Salmoiraghi, Freiberger and SNO-T, and even these perform very well on the bench.

Nevertheless, it is probably wise to approach a reading always from the same direction, preferably so the axial load is against a solid abutment rather than the spring and especially if the design has no axial preload spring.

Bill Morris
Pukenui
New Zealand
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