HP 54710A User's Reference Manual page 384

Histogram Menu
Histograms in the oscilloscope
Histograms in the oscilloscope
The oscilloscope has three features that use a specific data base. This data
base uses a different memory area than the waveform record for each
channel. The three features that use the data base are histograms, mask
testing, and color graded display. When any one of these three features are
turned on, the oscilloscope starts building the data base. The data base is the
size of the graticule area, which is 256 pixels high by 451 pixels wide. Behind
each pixel is a 16-bit counter. When color graded display, mask testing, or
histograms are turned on, a data base is built by incrementing the 16-bit
counters each time a pixel is hit by data from a channel or function. The
maximum count (saturation) for each counter is 65,535. You can check to
see if any of the counters are close to saturation by going to the display menu
and turning on the color graded display feature. The color graded display
menu uses colors to represent the number of hits on various areas of the
display.
The data base continues to build until the oscilloscope stops acquiring data
or all three functions (color graded display, mask testing, and histograms)
are turned off. The oscilloscope stops acquiring data when the power is
cycled, the Stop/Single hardkey is pressed, or the run until mode softkey
in the mask, limit test, or histograms menus is set to stop acquiring data after
a specified number of waveforms or samples are acquired.
You can clear the data base by pressing the clear display hardkey, cycling the
power, or turning off all three features that use the data base. The data base
does not differentiate waveforms from different channels or functions. If
three channels are turned on and the waveform from each channel happens
to light the same pixel at the same time, the counter is incremented by three.
However, it is not possible to tell how many hits came from each waveform.
You can separate waveforms by setting the display to two graphs or by
positioning the waveforms vertically with the channel offset. By separating
the waveforms you can avoid overlapping data in the data base caused by
multiple waveforms. Even if the display is set to show only the most recent
acquisition, the data base keeps track of all pixel hits while the data base is
building.
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