Subject: Re: Laser Trigon Sent: 5/2/07 9:29 am To: Carl & Barbara Sabanski, [EMAIL PROTECTED]
Carl wrote: > In terms of laser pointers, all are not created equal. I >have seen a red laser pointer in operation and is beam is elliptical. The main problem with budget laser pointers is that their ray is unlikely to be co-axial with the casing and over larger distances this can be a problem. Hard experience has taught me that big sundials are best laid out one hourline at a time by direct shadow observation against the clock or, at least, several intermediate hours set out against which to verify the trigon accuracy. Check the noon gap of any large sundial where the shadow is cast by the style edges. If the noon gap is parallel it was probably set out by calculation. If it narrows away from the origins it was set out by direct observation against the clock. It is the umbra/penumbra effect. Tony Moss --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial
