Local time is considered to be the time under consideration at the proposed building site. Many researchers favor using military time as a way of marking the track of the sun during the day. Using this notation, at the vernal equinox on March 21, and the autumnal equinox on Sept. 21, the 12-hour day starts at 0600 hours (6 a.m.), moves through 1200 hours (noon), and ends at 1800 hours (6 p.m.).
It is also very important to note that there is another time correction that must be considered. In the interest of convenience, the agreed upon "local time" of a given site is influenced by time zone, daylight savings time and other man-made decisions and demarcations. It is the time on your watch. The sun however does not recognize any of these man-made adjustments. According to the sun or "solar time", at any given point on the earth "solar noon" occurs at the instant that the sun is positioned due south of that specific geographic location. This means that "noon" occurs at an infinite number of different times as the point of consideration moves east to west around the globe. Solar noon occurs at a different time for you standing on the earth from your friend standing as little as one foot east of you. The significance of this is that the heliodon devices are marked in time markings that indicate SOLAR TIME. The solar time for your site may differ from the actual clock time by as much as plus or minus 45 minutes at a given time of year. The amount of variation constantly changes and is influenced by the time of year and your position on the earth. There are equations for reconciling solar time and local time and various times of the year in given locations. If your heliodon measurements are time critical, you should consider performing these calculations so that you understand that when you read 2 p.m. on the heliodon, it may not correspond to 2 p.m. at your site! In Muncie, throughout the year, solar time can vary between as much as 30 minutes before to 30 minutes after local clock time.
A web site containing a convenient on-line calculator for determining the local-solar time relationship can be found here: Sunangle Web Site