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The smaller tube on my O-K is 0.758" diameter .  That means circumference is 2.38" (0.758" x pi).  Ignoring the effects of it actually being a helix, that gives a scale length of 47.6" (20 x 2.38") for the 20 cycles I counted on mine.  I'd previously heard that the scale was equivalent to 42".  Accuracy to 3 significant near 10 and 4 near 1.

My 8" Atlas circular with a 30 cycle sprial is 4 significant digits from end to end.

Bob II

Re: Otis King Sight Reduction
From: Brad Morris
Date: 2017 Oct 11, 17:55 -0400

Greg

Otis King Cylindrical rules, with an effective scale length at 66 inches will certainly prove satisfactory.  A nominal linear slide rule will have scales in the 10 inch range (or perhaps a pinch more given the individual rule).  6 times longer length, given the same range of numerical values, affords better resolution in the scale markings, yielding less fudging and greater accuracy.

This applies to the Bygrave Cylindrical Slide Rule as well.  The scale normally applied across 10 inches is wrapped around and around the cylinders, for a scale length purported to be 590 inches (15 meters). Of course, it's a special purpose slide rule, leading to spherical triangle results accurate to 1-2 arcminutes!

The Fuller Cylindrical Slide Rule is also general purpose calculator, just like the Otis King in theme, yet larger.  The scale length here is purported to be 496 inches ( 12.6 meters).  Call it a 50 to 1 improvement in resolution!  Of course, it's a much larger device than the Otis King.

This is a "no brainer".  Of course the Otis King is acceptable.  I concurr!  Plus, they are much more affordable to folks than either the Fuller or the Bygrave.

Brad

On Oct 11, 2017 2:07 PM, "Greg Rudzinski" <NoReply_Rudzinski@fer3.com> wrote:

The attached PDF should be helpful for those attempting to restore an older Otis King calculator.

Greg Rudzinski

Attached File: 
Otis-King-Assembly.pdf