NavList:

Tony,

         Thanks for raising this topic and to Ed for his explanation. These arcane proportional logarithms are something I had not encountered before. Since you haven’t had an answer to your follow up question here’s what I notice.

Ed has clearly done the correct calculation but appears to have made a simple transcription error when writing it up and as you point out chose not to make use of the prop logs in the Almanac. Here’s a modified segment of the explanation at http://fer3.com/arc/m2.aspx/Lunars-how-use-proplog-tables-EdPopko-aug-2016-g36381

-------------------------------------------------------------------------------------------

Using your post data ...

12:00 UT, 84° 35'.2, PL 2620

pLogD =   2620

and ...

d is total change in LD distance from First time (12:00) to your unknown time of lunar sight
d = 84° 35.2' - 83° 00.0'
  = 1 35.2'
Looking 1 35.2' up in table ...
pLogd = 2766

Thus ...

--------------------------------------------------------------------------------------------------

The difference between 2623 calculated directly and 2620 from the Almanac propagates through and changes the final result slightly

Regards,

Robin Stuart