A flexible method of detecting coincidences and short time intervals has been devised in which a photo‐multiplier tube views the screen of a cathode‐ray tube. By using one pulse as initiator of a sweep and the other in vertical presentation, coincidences can be observed in a fixed portion of the screen while the remainder of the screen is masked off. In present use the method is limited only by the pulses available (5×10−8sec.). The method appears to be capable of extension to time intervals of the order of 9×10−10second or smaller.