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Thanks for the feedback, Tibor!

I went back and forth on which way the Log Haversine spiral should go (you can see some commits in the version history where I changed my mind).  In the end I decided that having the carries go in the same direction (inward for clockwise, outward for ccw) on both sides was easier to deal with than the opposite spiral.  As you point out, that is a place that errors can occur; one thing that I've experimented with is having a sliding marker on the cursor (in addition to the fixed ring markers in the photo) so that you don't have to keep it in your head.

One option would be to replace the lunar side of the sun wheel with the single LHA scale.  I'm not sure how many people are shooting lunars (I was inspired by reading about Frank's class to learn how to do it but haven't done it at sea yet), and as you also pointed out the accuracy of the lunar distance clearing computation is hard to get better than 1' of LD when rading from the linear haversine scale, which is around two minutes of chronometer error.  Since there is no spiral in the rough estimatation scales, it would be possible to include both Log and non-Log Haversines on the center section without too much ambiguity.  The major downside is that you do need to do the whole operation twice (although I find that I will often use the wheels twice or three times just to be sure that I get the same value anyway).

Regarding the 60 degree limitation: I'll be sailing around Iceland this summer so that will be a problem for me... I have a version that added a second cosine spiral for one of the outer rings, which allows sights up to 75 degrees, but with the complication of now having to deal with potentially extra carry operations.  Only one of the rings would need the second spiral, so it would squeee in between the two rings.

I'll play around with the rough computer idea and post an update.  Thanks for the suggestion!

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