10MHz clock which have ultra precision is used for the input clock. This clock is converted into 50Hz which is 1/200000 by CPLD (XC9536).
http://www.hobby-elec.org/e_pic6_7.htm
http://www.web-ee.com/Schematics/Nixie%20Clock/nixie.htm
http://www.interq.or.jp/japan/se-inoue/e_pic6_7.htm
video clock using a PIC16C61
http://www.brouhaha.com/~eric/pic/pictock.html
Seven LED spin, giving the illusion of numbers in the air
http://www.bobblick.com/techref/projects/propclock/propclock.html
based on PIC16F876
http://www.webx.dk/oz2cpu/clock/Nixie-Clock-Schematic-OZ2CPU.pdf
Two versions, one uses a PIC and can be activated in a single room, other uses a ST7 micro for a total of eight rooms
http://private.addcom.de/KeithWilson/Projects/speclo.htm
http://private.addcom.de/KeithWilson/Projects/caclo.htm