Histogram Traces (Pulse)
Menu Path:
A Histogram indicates how frequently a particular value is encountered in a trend line. Instead of points, histograms display evenly spaced bins. The x-axis of a histogram corresponds to the value of the metric and the y-axis indicates the probability of finding a trend data point in a particular range.
A histogram is calculated from all the data that has been accumulated for a metric since the last measurement restart, up to the internal buffer length. The Pulse measurement chooses a histogram bin width that is small enough so that you can see the shape of the histogram, but not so small that there are a large number of empty bins.
If you place a marker to read the value of a histogram bin, the probability you see (in percent) is the probability that the Y-axis value of the corresponding trend data falls in the range:
[x – d/2, x + d/2), where x is the bin x-axis value and d is the bin delta (x-axis distance between two bins)
Notice that the range includes the lower point, but not the upper point (which is included in the next bin’s range).
Histograms are reset whenever the measurement is restarted. Histograms are not reset when the measurement is paused, or trending is disabled during a running measurement, or trend removal settings are changed.
Histograms accumulate most trace indicators that happen during the measurement (as long as the measurement completes and produces table data). Trace indicators come from the Pulse table. The Sync Not Found indicator is not accumulated since the Pulse Table does not get calculated in this instance. The CAL? indicator is not accumulated while the measurement is running since the 89600 VSA software only checks for CAL status once the measurement pauses. In addition, DATA? is not accumulated.
Trend Removal
Since the histogram is calculated from trend lines after trend removal has been performed, histograms are affected by the trend removal settings as well. The annotation above the histogram trace shows the number of points used in calculating the histogram as well as any mean, slope, or 2nd order that was removed from the data.
Histogram Range Limit
In the Analysis > Statistics panel, you can select whether the range of the histogram is determined automatically or set to the min/max of the trend data (Histogram Range Limit = Full).
When determined automatically, values that are outside the histogram range are not shown in the bin percentages. In this case, the annotation above the histogram indicates what percentage of the points are outside the histogram range (“Outliers:”). In addition, in auto mode, the histogram is centered around the average of the trend line.
Refer to Statistics Enable for the associated Trend Line display control parameters.
See Also
