Hello John, In your analemmatic dial instructions in the table for de coordinates of the hour markers I found a type error: in the column of the Y-values 0.996 must be 0.966.
I calculated the declination values you use in the tangens function for the coordinates of the data scale (first values below). Compared to the average values (I found them, I do no more know where, on the world wide web) for the years 2000-2099 (second values below) there are significant differences. Jan. 1 -23,13 -22,97 Feb. 1 -17,30 -17,00 March 1 -8,00 -7,36 April 1 4,25 4,77 May 1 15,00 15,26 June 1 22,00 22,13 June 21 23,44 23,43 July 1 23,00 23,06 Aug. 1 18,00 17,85 Sept. 1 8,50 8,05 Oct. 1 -2,90 -3,42 Nov. 1 -14,00 -14,61 Dec. 1 -21,67 -21,88 Dec. 21 -23,44 -23,43 On a sundial in Cairo (Lat. 30°) with a width of 6 meter for instance the difference on March 1. and Nov. 1 results in a difference in distance of 3 cm on the data scale and a difference in read time of several minutes. That is to much for "the oldest an most accurate scientific instrument". Who gives us precise values for the sun declination? Willy john hoy wrote: > I've gotten a fair amount of email lately from people who want to make an > analemmatic dial but are not comfortable with technical or theoretical > explanations -- they just want a sundial. > > I've tried to prepare some simple, hopefully not confusing, instructions, > which I would like to invite any of you who are interested to review. I > will welcome any criticism or corrections. > > It's at > http://www.cyberspace.org/~jh/dial/analemmatic.html > > Thanks, > > John Hoy Content-Type: text/x-vcard; charset=us-ascii; name="willy.leenders.vcf" Content-Transfer-Encoding: 7bit Content-Description: Card for Willy Leenders Content-Disposition: attachment; filename="willy.leenders.vcf" Attachment converted: Macintosh HD:willy.leenders.vcf 1 (TEXT/ttxt) (0001F3C6)
