To establish a clock it is only necessary to set up a ring whose circumference has the desired period, draw the signal off at some point, and insert an electron. Diodes can be used to protect the clock, and to ensure a particular direction of circulation. More elaborate clocks can be constructed by spacing out several electrons within the same circumference.
WireWorld inherits the basic three-cell loop from the Zhabotinsky reactions, yielding all kinds of period-3 clocks. That is also the closest spacing that two electrons can have, but it is entirely too fast and dense for most applications.
A ring of four cells gives one of the smallest manageable clocks:
Figure: WireWorld clocks
However, loops yielding period six or even longer lead to more conservative constructions. Period six allows the inclusion of ultrafast period three subassemblies.
A clock seems to be the only way to create the boolean constant TRUE; once again it is worth emphasizing that the constant only appears at intervals and propagates with a finite velocity.