IIRC the Apple Newtons used a thermocoupler integrated into the LCD to help keep the contrast adjusted to the user-set level as the temperature of the device ch

IIRC the Apple Newtons used a thermocoupler integrated into the LCD to help keep the contrast adjusted to the user-set level as the temperature of the device changed. There was at least one application that would read the current contrast setting of the screen and infer the temperature. I don't remember it being super accurate but it worked. The Newtons had grayscale LCDs with manually adjusted contrast. The MP130 and later also had an electro-luminescent backlight but it was not always active. So the user contrast setting was very important to maintain for screen visibility.