NavList:

Thank you very much, Frank. Your proposed first method is ingeniously simple. Yes indeed—I have always eliminated the side error without analysing its effect on measured angle. After reading your answer I tried to imagine how the side error o 1’ affects the measured angle of lunar distance. Probably 2 seconds of arc, I think (see picture bellow)?

Your second method in my situation would not be practical because my metal sextant (USSR model SNO-M) is good instrument but I have noticed that on account of frequent transportations by car and in different temperatures  it gives slightly different IC values. Therefore I have no posibility to rely on the results of IC measurments which are made only once during a long period of time.

I would like to take opportunity and say a big thank to you, Frank, for your work.  The almanac, lunar calculator, your GPS Antispoof, managment of NavList etc. — all these things have become so ordinary for me, as a logical part of my hobby.

Modris Fersters

Sextant hobbyist from Latvia