The standard 5328A mainframe measures frequency, period, period average, time interval, time interval average, and ratio. A totalize function is also provided. The capabilities of the instrument are expanded (as shown in Table 1-3) by installing the options described in paragraph 1-17. The 5328A provides an 8-digit (9 with Option 030) LED display, display storage, and leading zero blanking. Decimal point and unit readouts are displayed automatically. Two independent selectable input channels are provided for time interval measurements. Each input channel has an attenuator, trigger slope selector, level control, ac-dc coupling, and an oscilloscope marker output. Rear panel connectors provide a gate output, a time base output and an input for an external frequency standard. An ARM switch on the rear panel allows arming by the signal being measured (switch OFF) or by another input signal (switch ON).