A secure content delivery or access method may include coordination among three devices such as servers\u2014a content management server, a delivery server, and an authorization server. Each delay cell has a biased pMOSFET to provide pull-up current and a biased nMOSFET to provide pull-down current. The presence of foreign material is determined when the off angle scattering response exceeds a predetermined threshold. The lighting state of the LED indicator indicates where the error has occurred in the computer system, so that a user can verify which element of the computer system has an error, without additionally adding a POST card to the computer system. The change from the first group of tips to the second group of tips occurs while the wafer is rotating.