The gClock is a class with two functions:
define, with related screen, coordinates and radius of the graphic, front and back colours, additional colours
display, with the values hour, minute, second
Note that the graphic is updated only if the value passed is different form previous value. This allows smoother graphics and fast drawing.
Typically, the clock refresh requires from 0 to 140 ms, depending on whether second, minute and hour have changed.