Being a Math teacher, here's my explanation - 360 degrees is a full circle possibly = to a full cycle of the sweep. When it only goes through the cycle 1/2 way = 1/2 of the cycle = 180.
As for pin jam = 90, I hadn't heard of it before, but here's my made up explanation. The pins are not at a 90 degree angle with the pinsetter, and need to be returned to the 90 degree angle.
That's my story and I'm sticking to it

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USBC Bronze Coach "I cannot change the direction of the wind but I can adjust my sails to reach my destination." Jimmy Dean
Quaker 10/93 - 4/07
Quaker Edited on 11/9/2008 12:34 PM