I might add, that you could combine all three time corrections into a single table or graph. (EOT, Longitude, and Daylight Saving Time). Then the sundial user would only have to do one single correction. But there's the minor problem that the dates for switching from Standard to Daylight Savings Time change each year (here in the US). Unfortunately, when congress passed the Daylight Savings legislation, they said that the switchover would be on the last or first Sunday of certain months instead of on certain dates. So you'd have to use the average switchover date in the table.
On second thought, this might be a bad idea because the time correction would be an hour off for a few days of some years! ----- Original Message ----- From: "John Carmichael" <[EMAIL PROTECTED]> To: "Sundial List" <sundial@rrz.uni-koeln.de> Sent: Thursday, July 08, 2004 9:44 AM Subject: EOT + Longitude Correction Table > Hello All, > > Some of you wrote me and seemed very confused with my inquiry about a way to > get a EOT table that is longitude corrected. You ot understand what I > wanted. So I'll try to explain it here. (thanks to everybody who sent me > info on this) > > Sample letter: > "I still cannot figure out your EoT problem; EoT does not depend on > longitude, it depends on an agreed absolute (GMT) and changes so little in > any time zone you cannot see the difference on a dial. Maybe I am missing > something, I often do these days." > > Yes, you are missing something. And it's so simple you will kick yourself. > You're thinking too deeply! I'll try to explain... > > Of course you are correct in implying that EOT values are "Universal" and > are basically the same all over the world, at any longitude or latitude and > on any given date. You can use the same EOT graph with almost any sundial > anywhere in the world. But you know that already. So far so good. > > But if somebody really wants to know "clock" time, then not only does he > have to correct his sundial readings for EOT, but he also has to correct for > his longitude (and Daylight Saving Time if applicable). This additional > longitude correction is expressed as a plus or minus value in minutes and > seconds. But you know this already. So far so good. > > Now this double correction is sometimes confusing to non-dialists (it's a > triple correction if one has to correct for Daylight Savings too). So to > reduce two time reading corrections into just one correction, you can add > the EOT correction to the longitude correction since both expressed in > minutes and seconds, and you come up with a new EOT graph or table that > incorporates the longitude time correction in its values. > > Now do you get it? Neat huh! > > For my sundial customers, I usually build the longitude correction directly > into my sundial faces so the customer doesn't have to do the longitude > correction, just the EOT correction. This combined EOT+Longitude Correction > Table is very useful if you have an antique pre-timezone sundial or any > sundial that doesn't have a built-in longitude correction. The downside is > that you have to make a unique customized EOT table for each sundial, > depending on its particular longitude. > > Hope this helps > > > > > - -
