I was about to make a competitive set for my Eelektross, so I went to Bulbapeidia to look up Eelektross's and its evolutionary line's learn sets and was thinking of making a mixed set with Coil and Zap Cannon in it (mixed set just because Coil also raises attack and defense too and I wanted Zap Cannon as a powerful STAB move). So how many times do I have to use Coil until it always hit?
Coil raises accuracy by 1.33 times, so-
Zap Cannons accuracy is 50 x 1.33 x 1.33 x 1.33 = 117(rounded)
So you would need to Coil 3 times.
Well if you use an Accuracy boosting move 3 times you get 2X Accuracy. So Zap Cannons accuracy would be 100% if you used coil 3 times. Hope I helped!