You need to turn the crank left and right to see how many degrees of slack you have.
The way to do this is to watch the rotor bug while turning the crank.
Turn the crank to the left untill the rotor bug moves ,then see how many degrees it turns the other way untill the rotor bug moves....................you will need to find the spec on how much is acceptable,but this is how you come up with that number or degree of slack.