There was a tool invented for the automotive oscilloscope that was basically an optical mouse encoder wheel attached to the end of a probe. The probe wheel was pressed against the belt to spin it. Lots of probes were killed due to butterfinger syndrome. Its digital output was converted to analog before put on the screen. This device, in concert with the traditional ignition pattern, would identify a weak cylinder/misfire based on crankshaft acceleration. It worked fairly well, provided you knew when and which cylinders were firing on the indicated pattern.

With the advent of misfire counters, this probe is now obsolete........but I still have mine. heh.
Figured I'd mention this tool in case anyone wanted to build one.