The timer has two modes of operation.
In mode one, the first beam interruption starts the timer and the next interruption stops the timer. It makes no difference on which of the two possible photogate inputs they occur.
In mode two, the timer measures the duration of the interruption. In this mode, however, one gate or the other must be selected.
The total count available is 9.999 seconds in 1 millisecond increments with a crystal-controlled accuracy of +1 count. The count may be allowed to accumulate on successive starts or can be reset to zero with the push-button. The display is a red LED with bright half-inch numerals.
The photogate and timer are ordered separately, with either one or two gates per timer. The tripod, post and clamp shown in photo are for demonstration purposes and are not included.