The ODial uses a separate outer hoop to mount a movable date wire and gnomon, relative to the fixed time scale. The date loop size was chosen to intersect the time scale at a 2 hour span. A 2 hour span can be accurately marked off on the time scale using a drawing compass set to the radius of the inside of the time scale. Bisecting the chord and drawing a line from the time cirle through the center of the chord sets the center of the date wire circle on the time scale. This is also useful for filling out the rest of the hour markings. The actual radius of the date wire circle will be the chord between adjacent hour markings 30 degrees apart or 2R(sin(30/2))=0.51763809021R. This provides a pleasing aspect ratio for the analemma plot and hardware. This is the ratio used in the analemma plotting equations and for the graphic.
    The November error is about 16 minutes and the error in February is about 14 minutes for a total of about 30 minutes. This dictates about a 15 degree rotation of the outer loop to correct for the solar to clock time discrepancy.
    With the maximum tilt of the earth being about 23.4334 degrees and a tangent of 0.4334, the length of the straight gnomon must be greater than 0.8668 times the diameter of the time circle to always cast a shadow on the time scale. Using a length equal to the diameter allows for some curl on the ends of the wire to prevent injury.
    The plot must be split at the equinox and flipped to correct for the repositioning of the analemma shelf in the spring and fall.
    If this design is followed, there is nothing to adjust except the scale factor, the aspect ration is fixed by the design. One is free to tinker with the source code for the plot and change anything desired, or course.