NavList:

Andrew,

Thanks for engaging with me around this design. 

While it is possible that my eyes are crossing as I stare at the rule, when I look at the S scale between 6 and 10 degrees, as well as T1/T2, I am counting 12 divisions of 5' each.

As for the method of graduation, when I am doing sight reduction or thinking of latitude/longitude, I am using degrees-minutes-tenths-of-a-minute, as in:

     53° 38.4' N    113° 46.1' W

For better or worse, my objective was to design the scales to accomodate this way of thinking.  That it is different from the more traditional ways of laying out scales on a slide rule (both on American and European rules) seemed to me to be a good thing rather than a bad one.  It is part of what makes this a *navigator's* slide rule.

I do recognize that in using a non-standard method for graduating the scales, I have just made the learning curve a bit steeper for the person who is accustomed to thinking, for instance, in decimal degrees.  Shikataganai (which is Japanese for "sometimes there is no one, perfect solution to a problem").

Bob