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    Re: Sighting errors
    From: Joel Lynn
    Date: 2019 Jan 7, 17:11 -0800

    Peter, 

       The mirror is 1mm thick, and mounted with double-sided tape. The Starrett is a four inch model. My sextants are both metal, one is a 1902 vintage Heath, and the other a 1945 Hughes. The Heath was cleaned, lubed, and adjusted by Weems & Plath in 1979. I've attempted the same with the Hughes, following "The Nautical Sextant". Its two mirrors seem fine.  Both sextants pretty much agree with each other. 

       If I superimpose the sun's images, the same error occurs. Consequently I'm not sure if Greg's suggestion applies. 

      My thin mirror could well be the culpret--maybe I should consider a Freiberger AH? Naturally, as soon as possible, I want to try your test method for flatness. 

       
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