The
Sundial Primercreated by Carl Sabanski |

Mean Solar Time = Apparent Solar Time + EoT but this convention is by no means universal and the opposite sign is used in modern almanacs. Irrespective of the sign convention adopted, the sundial will appear slow compared to the mean time in February, and fast in October/November. EoT varies continuously, but is usually tabulated for noon each day at a particular location.
The "Correct-A-Dial" Calculator was created to help you determine the value that must be added or subtracted from a sundial that indicates local apparent or solar time. This value includes the corrections for the Equation of Time and longitude. It can be used for any longitude. If you want to have this correction for only one location, let's say for your sundial, then you want the "Correct-A-Dial II". The "Correct-A-Dial II" is a modified graph of the Equation of Time that has blanks where you enter the values for the combined Equation of Time and longitude correction at a single location. Figure 1 illustrates the "Correct-A-Dial II".
The "Correct-A-Dial II" comes with a number of examples that will help you with the simple calculations that are required to find the values to fill in the blanks. You can get a pdf file of the "Correct-A-Dial II" right here. If you would prefer a completed "Correct-A-Dial II" they are available too! These are available at longitude intervals of 1/4°. This means that the longitude correction is to the nearest minute. To find the "Correct-A-Dial II" you need requires a little calculation as follows: a)
Longitude of Sundial: ____________ ° (W/E) It is important that you enter all west longitudes as positive values and east longitudes as negative values. The pdf file for the "Correct-A-Dial II" offered above provides examples of this calculation. When you obtain the
"Longitude Difference" round the value off to the nearest 1/4°
and get your completed
"Correct-A-Dial II" pdf file from the table below. Positive
values are for locations west of the local time zone meridian and negative
values for locations east. Cut it out and laminate it and it's good to go. Happy Dialling! |