I was referring to the ambient temp/temp of the refractometer, not the sample. I don't cool the sample. But if the ambient temps are too extreme and if I let the refractometer sit out in those temps, calibrate there, and use it, my readings are inaccurate.
Case in point the last two weekends when it was 35F in the garage where I brew. I left the refractometer in the laundry room right inside the door where it's normal room temp and I was good to go. I get the same type of inaccuracies in the summer when its' 110 in the garage.