Comparator with Internal Hysteresis
From Maxim note:


  Hysteresis is designed into most comparators, usually with a value of
  5mV to 10mV. Internal hysteresis helps the comparator avoid
  oscillation due to small amounts of parasitic feedback. Though
  sufficient to prevent the comparator from self-oscillating, such
  internal hysteresis can easily be swamped by any external noise of
  greater amplitude. In that case, you can improve performance by adding
  hysteresis externally.



Assuming Y > X, then the system hysteresis will be Y mV only.  
Assuming Y &lt; X, then the system hysteresis will be X mV only.