The quickest and best way to manage your boil is to wait till the element(s) are covered on your boil kettle during sparge and immediately set them to 100% on the panel. Once you have a rolling boil, drop it down to 75% and watch for a boil over. Depending on the strength of the beer (dissolved sugars in the wort) it can be set to as low as 50 or as high as 80 to maintain a good roll without causing a boil over.