NavList:

Dear Antoine,

I also recalculated the first lunar using Frank’s online calculator. I got the cleared LD excatly the same number as you: 80° 48,4’. And the time: 17:58:49 (only several seconds from your value).

I got latitude about 24° 02’N, slightly more to the north than your value (maybe because of some simplifications I used), but in general my results are very close to yours. Of course this latitude should not be considered as the latitude where the ship actually was. An error of several arcminutes is very possible. But we can say that something is slightly wrong with this latitude. May be navigator used noon’s latitude that was not corrected for distance made from noon. It correlates well with navigator’s approach to keep things simple. And the course and speed roughly confirms that.

But unfortunately our calculations say nothing about how accurat were the navigator’s lunar observations. We can only find how accurate results gave his lunar clearing approach and almanac data if compared to modern tools.

PS 1: Don’t thank me for publishing this 19. century lunar calculation example. It was Frank, who did it. J

PS2: Something is wrong with your email adress, when pasted in. You wrote your adress as: antoine.m.couette[at]club-internet.fr. Does it mean antoine.m.couette@club-internet.fr?

Best regards,
Modris