1. A method of input of a computing system including a touch sensing surface, the method comprising: detecting a plurality of contacts, including a first contact, a second contact, and a third contact, touching down on or near the surface, the detecting including determining a touchdown time of each of the contacts; evaluating the touchdown times based on a predetermined temporal threshold, the evaluating including determining that the difference between the touchdown times of the first and second contacts is less than the predetermined temporal threshold and determining that the difference between the touchdown times of the first and third contacts is greater than the predetermined temporal threshold; determining, based on the evaluation of the touchdown times, a synchronized set of the contacts concurrently touching the touch sensing surface, wherein the synchronized set includes the first and second contacts and excludes the third contact; and generating a first input of the computing system based on the synchronized set.