As the Z80 doesn't use dynamic registers (I think basically the only "modern" CPU to make this decision) it doesn't need a minimum clock signal speed to refresh

As the Z80 doesn't use dynamic registers (I think basically the only "modern" CPU to make this decision) it doesn't need a minimum clock signal speed to refresh the registers as every other CPU does. This means you can rig up a push button switch and manually advanced the clock one button press at a time. To me that's super cool. It also makes them really easy to debug.