NavList:

David,

You wrote:

...for the calculated LDs all you need is Dec and GHA. The GHA can be approximate. You pick a time  consistant with your DR.

Yes, that's basically right. Although, I wouldn't use the term "approximate" for the GHAs. You'll want to use the exact GHAs and declinations, typically for each whole hour (UT) before and after your observation. And yes, a good way to narrow down which UT hours those are is by using your DR longitude. (Or, of course, using a clock or watch set to UT to record the times of your observations. In this case, you'd probably be using the lunar to check the error of the timepiece as opposed to determining longitude.)

You continued:

[Calculating distances for each hour is] very easy for 21st century Lunerians with massive computing power in their pockets but probably  something a pen and paper navigator would avoid.

Keep in mind that when the first nautical almanacs were being published by Maskelyne, they included pre-calculated lunar distances for every three hours. So really, all of this work had already been done for the navigator. Of course now we can use a pocket calculator to find the distance, but even using tables such as Bruce Stark's, it's relatively painless.

You also asked:

How accurate must the  observed altitude be?

I can't give you an exact number here (perhaps Frank will chime in), but Bruce recommends trying to get them "...within 1' or 2' of the truth - especially if the distance is short." You can always experiment with different altitudes to see how this affects the result.

Regards,

Sean C.