A clock is just a very predictable oscillator

CLOCK is the one element in Boolflow that changes on its own, without any input: once started, it toggles between 0 and 1 automatically at whatever frequency is configured, with no INPUT switch or wiring needed to drive it. Every flip-flop, counter, and register article on this site assumes some CLOCK element is what's actually driving the CLK input under discussion.

Frequency is a simulation-speed knob, not a logic one

Changing a CLOCK's frequency changes how fast the simulation visibly ticks, but never what the circuit computes — a counter reaching 9 after ten rising edges does so whether those edges arrive once a second or a hundred times a second. Frequency only starts to matter once a circuit's timing has to relate to something outside the simulation, like a target baud rate for a UART.

One clock, many derived rates

Real designs rarely run every stage from the same raw clock frequency. Chain CLK_DIV blocks off one CLOCK to derive slower, related rates instead of adding a second independent oscillator — important, because two unrelated CLOCK elements driving different parts of the same circuit reintroduces exactly the crossing-clock-domain risk covered in synchronous design and metastability.

Try it yourself

Drive one CNT4 straight from a CLOCK element and a second CNT4 from that same CLOCK divided by 4 through two chained CLK_DIV blocks in the circuit editor, and confirm the second counter advances by 1 for every 4 ticks of the first.