Timing Light Accuracy

I found a buddy with a timing light. I'm going to snag it this weekend and check it against mine. I'll report back with results.



It does not kick back at all with 30-32* initial - even when hot. Cranking compression is 162-168 lbs. I've run it WOT with up to 40* total (with my light) and no signs of detonation.
With what fuel,heads, and Q; might I ask?