# One Level

The One Level is a measure of the mean value of the logical 1 of an eye diagram. Annotation labels are placed at the logical 1 level. This measurement is made in a section of the eye referred to as the eye window boundaries. The default value for the NRZ eye window is the central 20% of the symbol period.

A histogram is constructed using the sampled portion of the eye diagram within the eye window. This histogram is comprised of data points from only the upper half of the eye diagram. The histogram mean is located.

The following graphic illustrates how the histogram is constructed on an eye diagram that is pattern dependent. Pattern dependency is the behavior of a waveform as it is influenced by the preceding data pattern. For example, a logic level one that follows a logic level zero may have a different amplitude than a logic level one that follows a previously generated logic level one.

You will notice when there is a vertical spreading to waveform and you are in gray scale display mode, some regions of the waveform are brighter in color than others. The brighter areas indicate a higher number of hits or sampled data points. The one level is equal to the mean of the histogram. All data at the zero level is disregarded.

This measurement applies to NRZ waveforms and not to PAM waveforms.

## Configurable Measurement Parameters

This measurement is affected by the following setting (choose Measure > Thresholds...):

- Eye tab

## To measure

1. Click the measurement toolbar's Eye Meas tab.
2. Click Auto Scale in the menu bar.
3. Click the More buttons to locate the One Level button.
4. Click the button.

## SCPI Command

`:MEASure:EYE:OLEVel`