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George,

Great story;-) When I first calibrated my Sunrule I went through a
similar process except that instead of a horse trough I used a distant
mountain peak. The baseline of the Sunrule is ball chain with each
ball 3mm from the next. I kept cutting off balls until the Sunrule
matched my sextant reading.

Greg

On Jun 5, 4:20�pm, "George Huxtable"  wrote:
> About calibrating a cross-staff: I have this little scene in my mind of how
> a cross-staff maker might ply his trade.
>
> The erstwhile navigator enters, saying that he wishes to buy. The proprietor
> fetches one of his stock out of the window. All these stock items have been
> made with the staff a bit extra-long.
>
> "Stand exactly at this spot, the navigator is told, and with this instrument
> held by your eye, tell me the angle you make it between yonder horse-trough
> in the yard, and the baker's chimneytop across the alley."
>
> and a moment later- "twenty two degrees and fortytwo minutes, you say? I'll
> soon fix that". He takes it into his workshop, and knowing that the angle
> should be 23� 15', can work out exactly how much to remove from the end of
> the staff to bring the reading up to scratch.
>
> The mariner is asked to try again, and presuming that his reading is now the
> correct one, money changes hands, and both parties are happy, with the
> instrument now tailored to suit his own skull dimensions..
>
> This is a scene that could be repeated over many years, as long as nobody
> shifted the horse-trough.
>
> That's just imagination. I have no idea whether that's the way it was done,
> but it's possible.
>
> George.
>
> contact George Huxtable, at �geo...@hux.me.uk
> or at +44 1865 820222 (from UK, 01865 820222)
> or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
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