The Hewlett-Packard Model 5315A and 5315B are universal counters, measuring signals over a range from 0.1 Hz to 100 MHz. The 5315A/B measures Frequency, Period, Time Interval, Time Interval Average, Time Interval Holdoff (Delay), and Ratio. A Totalize function with manual or external gating is also provided. All measurements except Totalize are displayed in engineer-ing notation with up to eight digits of resolution.