原理果然就是这样：
the pc board holds a switching power supply, a crystal-controlled microcontroller
for generating the timing and scanning the digits, and an analog circle generator
system to draw the digits. it makes circles directly from sine and cosine waves.
that's why the curves look so clean.
the drawing of the digits is done in segments, each segment being composed of an arc,
circle or line. angled lines are made by putting the same cosine wave onto both
the x and y deflection plates.
the display repetition rate is synchronized to the power line frequency by the
microprocessor to prevent image 'swimming' in the presence of strong ac fields.
this allows the crt to be free of magnetic shielding, which would add to the cost
and detract from the beauty of the clock.
this clock has a professionally made pc board to hold the electronics. the cabinet
is made by a local plastics fabrication company. all the parts are currently produced.
