# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Bygrave Scale Lengths
From: Brad Morris
Date: 2013 Jan 30, 09:19 -0500

Hi Gary

Image 122161.img_2160.jpg tells the tale!

In it, we see the rules for using the device.  Within those rules, we see the standard admonishments for the MHR1, with one major and glaring change.  In German, we have:

Bei d nahe 0 oder t nahe 0 und 90  verwende F-Tafel

Which I loosely translate to:

Do not use the slide rule (F-Tafel) when declination is near zero deg or when the hour angle is near 0 or 90 deg.

The is no longer any numerical prohibition like 0 deg 20 min or 89 deg 40 min.  It just says "near" (nahe).  This could be understood to say the same thing, since 20 min is near to zero.

But given the precise directions of the MHR1, I would like to think that near now means that the scale has been extended downwards and upwards, as we have discussed, towards 0 and 90 deg.  To what value?  The images do not reveal this data point.  Pity.  I'd like to think that it went to within an arc minute, the trick of a tiny offset to include 0 deg 90 deg not withstanding.

What do you make of the conversion table, the adjustment knobs and the magnifying glass?  Magnifiers are typically associated with verniers and fine graduations.

Regards
Brad

On Jan 30, 2013 12:39 AM, "Gary LaPook" <garylapook---.net> wrote:

I am attaching some photos I took of the MHR2 in London in 2009.

gl

+++++++++

I would be very curious to see what the scale lengths and operating ranges of the MHR2 table top calculator. Ronald - Do you know these values?

++++++
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