Once you have found your latitude, subtract the number from 90 degrees to determine your colatitude. This will be the angle you will use in the construction of your dial. For instance, here in southwest Iowa in the US, my latitude is about 41 degrees: 90 - 41 = 49. My actual sundial is constructed with an angle of 49 degrees. [Another way to think about it - the gnomon (the shaft at the top that casts the shadow on the dial) in an equatorial sundial is parallel to the earth's axis]

Building the Dial
The LDraw file for the construction of this dial can be downloaded here.

The angle of the arms is adjusted by sliding the vertical support axle along a horizontal axle in the base. This construction allows for a wide range of angles, and can easily be lengthened, if necessary, to accomodate extreme latitudes. I held a protractor upright alongside the finished model and slid the support until the arms were at the proper angle, then held the support axle in place with bushings.

Reading the Time
Once you have completed and set the angle of your dial, it's ready to use. Place it on a level surface with the gnomon pointing north (or south, in the southern hemisphere).

This dial takes advantage of the fact that the tread on the 81.6 x 15 Lego tire is divided into 48 roughly equal sections. The dial face represents 24 hours, which means that two sections of tread equal one hour. In other words, the shadow of the gnomon will move exactly two sections in one hour (and of course one section in one half hour).

Note Since the sun is above the equator half the year and below it the other half, your dial can be read on the underside face half the year, and on the top face the rest of the time.

To set the dial to local time, rotate the tire on the wheel so the shadow of the gnomon falls exactly on one of the lines between tread sections at a known time. You may wish to mark the tire at this point, and at other hour lines (I personally can't bring myself to mark up my Lego pieces. If you aren't a "purist" you can easily draw a dial face on paper and place it on the dial. Simply make a circle and divide it into 24 equal sections).

If you check your dial from day to day, you will notice it drifting in accuracy when compared to a watch or clock. This is because solar days are not all equal in length throughout the year. The difference between sundial time and mean time as shown on a clock is known as the equation of time. This difference changes throughout the year, and from year to year, and can be as much as 16 minutes. If you live in North America and have a current copy of the Farmers Almanac, you will find the equation of time listed for each day of the year. Or, you may simply check your sundial against a clock every week or so and re-set it. This will keep it accurate to within a few minutes.

To learn more about this type of sundial, and several others, I recommend Sundials: Their Theory and Construction by Albert E. Waugh (Dover, ISBN 0486229475)