Used
Actron Kal Equip Spark Analyzer 2969 units
are now pretty cheap.

https://www.ebay.com/itm/Kal-Equip-Spark...5.m43663.l10137

When they dropped below $50
I bought a second one
so I could easily compare the:

Peak KV
Burn KV
Burn time in milliseconds

On the wires to plugs on two different cylinders.

These simple to use little meters help track down ignition gremlins

Oscilloscope units that would display traces from all eight cylinders at once
Would be better
But they are bulky and much more expensive.