Snap on something?

if it only measures the ignition pulse and shows each coil strike as a sharp spike (4-6-8 at a time across the board) then possibly that is all it takes. a dead cylinder (low psi) would show a higher spark (less resistance). I think that's how it would measure cylinder health. Could be *** backwards but I know MSD publishes a 'hotter' spark to ignite "higher cylinder pressures" . Same way that ignition box works, ...Jacobs!