Circuit: non-inverting comparator, signal into the (−) input, feedback resistor R2 from output to the (+) input, R1 from the (+) input to ground. Formulas: V_UT = V_OH×R1/(R1+R2), V_LT = V_OL×R1/(R1+R2). The output only switches HIGH→LOW when the input rises above V_UT, and LOW→HIGH when it falls below V_LT — the gap between them rejects noise near the threshold that would otherwise cause chattering on a plain (non-hysteresis) comparator.