This is a type of non-planar portable clock. It is constructed using a cylinder with a vertical axis, with the gnomon that is perpendicular to this axis but also mobile. The gnomon must be rotated around the cylinder until it aligns with the date of the reading.
For this reason, this clock type doesn't have a calendar function. The calendar line is drawn on the upper part only to place the gnomon appropriately.
To read the correct time, the gnomon must first be set to the correct date and then the entire sundial turned toward the sun until the shadow of the gnomon becomes a completely vertical line.
This sundial includes a calendar, and the proper corrections for longitude, the equation of time, and for daylight savings time, in order to obtain the correct civil time.
The geometric dimensions of the clock used in the program are input in the screen DIMENSIONS.
Being a portable type clock, clock curves corresponding to a half year (summer-autumn and winter-spring) are placed on each half of the cylinder. In this way one clock can be comfortably used during the entire year.
NOTE: With this clock type we can obtain another subtype of the shepherd's sundial, the plane shepherd's sundial directly. Instead of drawing the curves on the cylinder, they can be drawn on a larger plane. In place of a gnomon, a visor projecting lip is attached along the top of the entire clock plane edge perpendicular to the clock face. The projecting lip extends the same distance from the clock plane as a typical gnomon. To read the time the entire sundial is aligned with the sun and the time is read on the clock
face.
