NavList:

Yes, that's quite true and D. Walden did post a link to that book in his message 6273. The question in my mind is no longer how to use the device since D. Walden provided enough information in his posts to thoroughly educate us on it's operation but simply whether this device caught on in practical use and, if not, why?.

Given the number of list members that have submitted very informative posts related to the Bygrave slide rule I would like to generalize the question to ask why didn't mechanical sight reduction devices ever catch on with the popularity of inspection tables. I would venture to guess that either the Poor or the Bygrave slide rule could have been produced economically enough to sell them at a marketable price.

I would be interested to hear opininons about what prevented slide rules from catching on. One could argue that the Bygrave and the Poor device are really very different animals since a Bygrave should give a substantially more precise result but I think the Poor device might have found a niche as well. By the 1940's or '50's it should have been possible to mass produce a Poor slide rule and sell them for a price that would make it reasonable for most air navigators to carry one. Even today, I'd spend 75-100 dollars for a modern Bygrave and $20 or $30 for a plastic Poor computer. That's in the range of inspection tables so I don't think I'd be unique in spending that kind of money for one more option to play with.

I accept as a given that slide rules provide a less precise solution than inpection tables but there seem to be enough advantages to balance that out for many applications. A slide rule can be made from water proof materials, a slide rule can be significantly lighter and more compact and they may be faster when one is comfortable with their use.

Was this simple reluctance to try something different or did a fair sample of the navigating population give these devices an honest trial and then reject them based on objective results showing that inspection tables provided a more accurate solution fast enough to outway the slide rule advantages in most applications.

Chuck Griffiths
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