If a T1 ‑ 1.544 Mb/s BITS (Building Integrated Timing Source) reference clock is available, then it can be used to measure clock slips and frame slips on the circuit under test. If two or more T1 ‑ 1.544 Mb/s circuits are present, then one of these can be used as a reference. The reference circuit (in this configuration) should be out-of-service because it will be terminated by the clock recovery circuit in the instrument.

To count clock slips, connect the reference clock to the Ext Trigger In connector on the instrument. The presence of the clock is automatically detected, and when a measurement is started, the number of clock slips and frame slips are reported. When the clock frequencies are very close, the clock slip count will hover around zero. If the frequency of the circuit under test is higher than the reference frequency, then the count will grow positive. If the frequency of the circuit under test is lower than the reference frequency, then the count will grow negative. One frame slip is counted for 193 clock slips.

If data resolution is set to a small value, then you can zoom in to see in detail when faults have occurred. However, small resolution takes up larger file sizes when saved. The maximum number of records is capped at 86,400, so if the user is interested in history longer than one day, then the resolution must be set higher than one second. If the data resolution is changed, then the entire histogram must be reset.

The display window is the length of time shown on the histogram screen. More data may be stored than is shown. This parameter allows a user to zoom in or zoom out to see either more time on the screen or more resolution. The minimum and maximum values are based upon the data resolution.

Turning the rotary knob while in the Histogram view scrolls a vertical yellow marker line across the histogram graph.

Time offset is the offset in time of the right side of the screen from the start of the measurement. The screen may be moved left or right with this parameter. Using this feature together with a small display window provides the ability to zoom in on an event that happened some time in the past.

If Relative is selected (underlined), then the histogram axis will be labeled with time since the start of the measurement record.

If Absolute is selected, then the histogram axis will be labeled with absolute times that are based on the system clock.