curve tracer and capacitor question

i saw an electronics repair technician today testing for bad electrolytic caps. he was using a huntron tracker 2000 curve tracer. i was kinda confused because he was putting one lead on the leg of the capacitor and the other lead on the metal casing on top of the cap. if it is an ellipse it is good, any other waveform means its bad. the thing i was confused about was why he was putting a lead on the casing of the cap? i just measured from casing to each leg with my ohm meter and im getting double digit Megaohms. this shows that the case is NOT in common with either leg. Please Explain!!TY!!

 

I have attached a manual for a huntron tracker. Not your model number but it explains the waveforms.

 

thanks for the reply. but my question is, why is he touching the casing of the capacitor if the casing is not common with either lead?

 

I find that strangely disturbing!
Occasionally,you will find an Electrolytic cap where the case is connected to one side of the capacitor,but it is not common,except in the case of multiple caps in one package.

I have never thought Huntron Trackers were worth using,but others swear by them,& seem to have good results.

 

I have come across some electrolytic capacitors where the "-" lead is tied to the body. These have mostly been "memory" capacitors, like 5.5V 0.1uF... Most of the time though the leads are isolated from the body.

 

As an addition to my earlier comments:

Single Electrolytics with one side connected to the case were commonly used as filter capacitors back in the days of "5 valve mantel radios"(At least,in Australia).
It's so long ago,I had forgotten them!