When using a scope test under load. I compared to the building power. Just make sure to have the scope plugged into the generator power because the neutral or grounds are tied together in the scopeBesides checking the voltage and frequency from your multimeter, how could you determine if the generator output is clean. I haven't used an o-scope since trade school, and wouldn't know what to look for, but I do have access to a decent one. It's a 1750 kw genset powered by a cat and just recently when testing it the ats was slow to sync.
First time poster, but long time follower.