NavList:

David Iwancio, you wrote:
"Here in the eastern US, on land, three lines from a handheld sextant can generally determine which county I'm in (10's of miles across); more lines can help confirm my county, increasing your confidence, but (all things being equal) I still won't be able to establish my town or postcode (1's of miles across or smaller) with any reasonable confidence"

Ack, what?? Wait, seriously... what?!? On land, with a decent handheld sextant, you should be able to get a position fix from just two sights to within a mile and with multiple sights you can easily reduce that to half a mile, repeatably, reliably, and confidently. Are you using some ultra-cheap sextant, or maybe a cross-staff? Or perhaps a sextant that's poorly adjusted? Or maybe... are you just doing it wrong?? There's no way that you should count tens of miles of error as anything but garbage results. I'm not kidding when I say "garbage results". Either you're just rhetorically exaggerating (and fine, if so), or there's something very, very wrong here!

You also wrote:
"However, truly random errors are not the only kind of error to worry about; there are also constant errors. If you're dealing with, for example, an unknown index error or unknown dip/refraction error ..."

Yes, those are systematic errors, and they have to be handled differently. In fact, taking multiple sights, like five each, on three stars, is an excellent way to detect and quantify systematic error, and then it can be corrected for. There are well-established procedures for this. In fact, we can treat constant offset in altitudes (index error + dip) as an unknown in the sight reduction process, if we have enough sights. This isn't at all difficult.

All that said, I do agree with you on the general point that taking extra sights is frequently overkill with manual celestial navigation. Nonetheless, a good navigator should probably aspire to understand the principles and be able to apply them when useful, right? There's surely no harm in more data. More data is always better. The question is, how do we use it to our benefit?

Frank Reed