On the pedalboard is a delay pedal with tap-tempo. Setting the tempo and turning the pedal on and off can be a little fussy since they’re both done with the same footswitch.
Put the pedal in a loop. You can bypass the pedal while setting the tap tempo, so while you’re trying to get the tempo just right the audience doesn’t have to hear.
The loop is passive, but since it’s always going to be mounted on a pedal board there’s a power jack and an LED so the guitarist knows when the loop is active. The last trick was to put it in the smallest possible box, so it doesn’t waste any precious space on the board.