Comparator with Hysteresis_Design Calculations
short answer is
If you put in any equation you should get same Vref value, if the calculations are correct.
few corrections.
Lets say assume Initially Vin started from 0V, Vout initial state will be Ov (GND or Vee),
as voltage starts increasing to Vih =1.3V we should see Vout switching to Vcc, But before that Vout = 0V.
So, for Vinh =1.3V equation will be
VthU = VinH(=1.3V) * R2/(R2+R1)  this is also same Vref ---&gt; Eq 1.
On the reverse side,
Now Vout = Vcc(high) and Vin is coming down to 0V ,
when VinL =1.2V Vout switches to 0V,Before that Vout is Vcc.
So, for VinL = 1.2V equation will be
VthL = VinL(=1.2V) * R2/(R2+R1) + Vcc * R1/(R2+R1) = Vref ---&gt; Eq 2
Now after equating Eq 1 &amp; 2 and solving for relation between R1 &amp; R2
we will get R2 = 33 R1.
Select R1 &amp; R2 based on your op-amp selection, I am not selecting them.
Now you put this R1,R2 relation in any equation, we should get Vref ~ 1.262V.