# Eye Height

Eye Height is the measured eye height:

> Eye height = (one level – 0.5 TI_b(ones)) – (zero level + 0.5 TI_t(zeros))

The nominal one level is the "average" of the high level. Same for the nominal zero level. The eye height must be smaller than the difference of the nominal values because these values do not measure noise. The TI (total interference) of the one level is the noise above and below the one level. Same for the zero level.

For a given level, TI is computed using a noise histogram and the dual-dirac model. If the histogram is asymmetric, the noise above the nominal level can be different than the noise below the nominal level.

Because eye height cares about the noise "towards the center" of the eye, TI uses the side of the histogram that goes "into" the eye. So, TI uses the bottom half of the histogram on the one level, denoted as TI_b, and the top half of the histogram on the zero level, denoted as TI_t (note that these values are computed internally but not reported). The (one level – 0.5 TI_b(ones)) portion is the amount of eye closure from the one level, and the (zero level + 0.5 TI_t(zeros)) portion is the amount of eye closure from the zero level. The eye height is the distance between them.

Oscilloscope random noise that is removed from the noise measurements is also removed from the eye height. This means the eye height may report a different result than observed in the plotted real-time eye.