I found a problem with the analemmatic design spreadsheet that I distributed this year at the NASS conference and earlier to subscribers of this list. In the most widely distributed version, for a longitude correction of less than 30 minutes, the table and charts show only the half hour times and not the full hours. When you tested the spreadsheet for your location, you must have wondered why I would only calculate the half hours. I am not a Newfie.* There is a another explanation.
The problem is a hangover from earlier versions that tabulated the hours and half hours. The bug is easy to fix. In cell A24, changes the 30s to 60s, so A24 will read "=A23+(60-MOD(A23*24*60,60))24/60" If you want both the hours and half hours tabulated, leave cell A24 alone and change the increment in the following A column cells to 1/24 to 1/48. For example, change A25 to "=A24+1/24" to "=a24+1/48" and copy this to the other relevant cells. Note the increment is negative for the AM part of the table. There is also an error in cell A34. This should be identical to A23, the local noon start point: "=0.5+D12*((B9/360)-(E11-1)/24". I know there are other bugs in the program that my tolerant fiddling will never find. Let me know what your experiences and problems have been. I am still willing to provide copies of the latest version on request. It is a 108kb Excel spreadsheet. The companion to this spreadsheet is the 78kb Powerpoint file containing the slides for the NASS presentation. I am happy to sent this out to any who can view Powerpoint files (.ppt). The abstract follows. "How Long Is My Shadow? The use of Declination Lines in the Design of Analemmatic Sundials" "When a person stands on the zodiac of an analemmatic sundial and acts as the gnomon, it is important for the tip of the shadow to be close to the time marker. Since the shadow length varies dramatically with date (declination) and time (altitude), it is important to consider when the dial is most often used and by whom. The typical shadow length should determine the size and layout of the dial. A computer spreadsheet was developed to optimize the design of an interactive analemmatic dial for the Calgary Science Center. For the specific latitude and longitude, the spreadsheet calculates the hour angles and coordinates of the zodiac and the time markers on the ellipse. From the solar altitude and azimuth of specified dates, declination lines are also calculated and plotted for typical gnomon heights. The presentation covers the design of analemmatic dials, describes the development of the spreadsheet, shows the design graphs and records the construction and use of the dial." The records of construction and use are 35mm slides photographs and are not available for distribution, but I hear that Ken Clark has the audio record. Roger Bailey Walking Shadow Designs N 51 W 115 * Newfoundland continues to be one of the few parts of the world that uses a half hour time zone. Radio and TV announcements on CBC give the program times across Canada and then add " one half hour later in Newfoundland".
