“The instrument…was artfully designed by Richard Schmoyer of Landisville, Pennsylvania. The gnomon on its axis is cut with a curiously curved slot through which the sun shines on the hour scale. The curve of the slot is engineered in such fashion as to make allowance for the equation of time, and other adjustments are included for the latitude and for the longitude correction as well as for shifting to daylight saving time in season. Either of these dials is as accurate as most pocket watches.”
Waugh, Albert E. 1973. Sundials: Their Theory and Construction. New York: Dover Publications.