"within 60 of 30" would mean 330 to 90, or 60 degrees in each direction from 30. So it probably is easier for you to just use the "is between angles" condition instead.
I don't understand your last question. The equation is:
speed = sqrt(2*deceleration*degreesToMove)
It calculates the speed needed so when using a certain deceleration it will stop after rotating degreesToMove degrees. The speed will be higher for higher values of deceleration and degreesToMove.
I would like that the spinner starts fast (750) but just turn 5 or 7 times and stop in the angle that I defined. Is it possible?