NavList:

In my post a few minutes ago, I mentioned the 3:4:5 issue I brought up previously. Just so that there's no confusion, I was referring to my 3:4:5 triangle topic that I started about two weeks ago in this post. Just to distinguish it from today's topic which spins off from that earlier discussion...

Some of you may be wondering why I started today's topic. It's not just theoretical chatter. This is an issue that can have measurable impact in coastal piloting and certainly in coastal surveying work. The triangle scenario I described earlier today is just an example of an observer with a sextant measuring the angle between two visible, well-defined objects at reasonable viewing distances (close to 6 and 10 nautical miles in the case as described). But the difference between the angle we naively calculate --as determined by various common methods-- and the true angle that we would observe and can calculate easily if we're careful is a substantial fraction of one degree. It's something you can see easily with a sextant.

Frank Reed
Clockwork Mapping / ReedNavigation.com
Conanicut Island USA