Part of the “vibe” of a Clavinet is that it is an imperfect and “human” instrument. If you play hard and really smack the keys, the strings stretch just a tiny bit sharp and then settle back.
The Realism control, found in the Clavinet and Vibanet Patches, emulates what occurs naturally when playing the real thing. The knob controls how much the tuning is affected by velocity. Small random pitch inconsistencies are introduced at lower values, while turning the knob further to the right makes the tuning sharper at higher velocities. With the knob all the way to the left, the instrument remains perfectly in tune.