You don't mean 'floating', you mean switching. And it's just a comparator, not a Schmitt trigger, as @ThePhoton notes.
PR1 is the collector of a bipolar transistor with the emitter grounded (through a very low value - 4\$\Omega\$ - resistor. It has 4.7K to 10V, so about 2.1mA is flowing into the collector. Vce of a saturated transistor would typically be in that range (< 100mV) but it will not be exactly zero. From the datasheet:
For example, take a 2N3904 under similar conditions with 100uA base current:
simulate this circuit – Schematic created using CircuitLab
If you run the above simulation you'll find the collector voltage is around 63mV.