PETG glass transition temperature?

Well unless you check your bed temperature you will never know, and your actually not printing on glass so to speak. The TAZ printer beds vary in temperature difference across the bed, use a IR thermometer to check. I find with the PEI material the bed is routinely 10 C under the displayed on the LCD readout. I set mine at 90 - 100 C and never have a problem with PETG.