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As Peter says, there was some discussion of the Bygrave navigational slide 
rule perhaps two years ago....? (The archives will have it.) Zvi Doron, 
sometime member of the list, set about making a copy. I think a couple of 
other list members made copies. Just recently, I also made a copy which 
turned out pretty well.

The slide rules Zvi Doron and I made were actually more a copy of the 
Besteck-H�henrechenschieber MHR1, (literal translation - �Height Calculator 
Slide Set MHR1�) which is the German model to which Peter referred. It was 
made just before and during the war by Dennert & Pape.

I wrote an article on the Bygrave slide rule which is in the current issue 
of "Navigator's Newsletter". As research for the article I went down to 
London to the Science Museum and the National Maritime Museum (or rather, 
the respositories of both these museums where items not on view are stored) 
to look at examples of these instruments. The MHR 1 is obviously a 
derivative of the Bygrave in that it is dimensionally almost exactly the 
same and the scales are laid out in exactly the same way. The only major 
difference is that the inner scale on the MHR 1 is logs of cotangents 
rather than tangents as on the Bygrave. (Why Dennart & Pape should have 
made this change escapes me - possibly to get around Bygrave's patent.) It 
is certainly much better made than the Bygrave and is probably more 
accurate due to the use of  hairline cursor screens rather than metal 
pointers, as used on the Bygrave.

To say the MHR 1 is "the finest cylindrical slide rule made" is perhaps 
misleading, in that the slide rule is dedicated to the purpose of sight 
reduction calculations. The scales are log cotangents and log cosines and 
so it would not be of much good for anything else. It is difficult on a 
cylindrical slide rule to have multiple scales, such as you find on the 
usual linear slide rules which might have anything up to ten different 
scales to use as required. So cylindrical slide rules are not well suited 
for use as general purpose slide rules. But the accuracy of a slide rule is 
dependent on the length of the scale and this is where a cylindrical slide 
rule wins hands down. The log tangent scale on the Bygrave, for example, is 
over 20 feet long!

I have been keeping a watch on ebay, but no examples of these slide rules 
seem to come up for auction, from which I conclude that they are pretty 
rare. If one did come up, it would fetch kilo-bucks for sure.

Geoffrey Kolbe

At 02:48 05/11/2006, Peter Fogg wrote:


>Occasionally in the past cylindrical slide rules have been mentioned
>here, eg; the one made by Bygrave.
>http://www.quadibloc.com/math/sr03.htm
>
>I understand that this design was taken up and improved by a German
>manufacturer, and that this German model (unsure of name) is perhaps
>the finest cylindrical slide rule made.
>
>Does anyone know more about this? Does anyone possess one?
>
>

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