I haven't been able to solve them yet. The real one is the following.
Hi, Dave > > I only have Compendia back to the first Digital version, in 1995(1994?). >I know what a "spider" dial is and looks like, but what was the effect of >the CD, other than the pretty diffraction patterns? Possibly, a spider >dial with no vertical gnomon? That would work well, for sure! > > Yes. If you hold a CD in the sunlight you'll see a brilliant diametral straight line pointing towards the Sun. This way you can draw in the CD surface the grid of ANY azimuthal sundial to know the hour. Reversely, if you know the hour and the date you can know the Sun's azimuth and the direction of the true North. From them you can easily calculate the declination of any wall. It's just a simple substraction of angles! Perhaps for these purposes it would be better to use a simple azimuthal sundial (see Helmut's Sonne programme) than a 'spider' or Oughtred sundial, because it is easier to interpolate the dates. Cheers, Anselmo PS.: By the way, what has become of the Abu Dabhi sundial? -
