The performance of two synchronisation schemes is compared. One scheme uses a fixed-period clock with the allowable resolution time of the synchronising flip-flop being one clock period, the other scheme uses a clock with extensible clock-pulse recurrence time and a special flip-flop with an additional output,M, which is asserted whenever the flip-flop is in the metastable state. By asserting the PAUSE input to the clock, clock-pulse generation is inhibited. TheMoutputs of the rank of flip-flops are collectively ORed to drive the PAUSE input of the clock, thus pausing clock-pulse generation when one or more of them is in the metastable state. A system using the first scheme fails when conflicting actions are taken by its components, owing to inconsistent interpretation of the outputs of the flip-flops that are in the metastable state. In the second scheme, a system fails when the job execution time exceeds a specified upper bound, owing to extension in clock pulse recurrence times. If the path delays from theMoutputs to the PAUSE input of the pausable clock are small, the second scheme performs better. However, its performance degrades exponentially as the delays increase.