NavList:

Hello, David C,

You wrote: "This then raises a question - if shipmasters took the easy way out and took their chronometers off ship to be rated  then why would they  bother with lunars?"

Lunars were the only available method for rough chronometer check during very long passages, when the ship was far away from the land (this, of course, refers to pre-radio era; more typical for slow sailing ships). The rate of the timepiece was calculated using 2 lunar observation sets with about 8-10day interval. Observer calculated the error of chronometer on those two dates and found the rate. Of course, another question is the accuracy of such a rating method (even the lunar distance fan Chauvenete expected 20 seconds of time possible error even under excelent conditions). And I  doubt that this method was widely practiced. But the artifical horizon usage for rating in a maner discussed previously in NavList, could be practiced only on land. But these are not lunar observations.

Modris Fersters

PS Your published materials on this topic are really very interesting.