Our windowpane thermometer is 7" across, with extra large numerals that can be easily read from right across a room. The clear vinyl dial clings electrostatically to the outside of your window (like a car tax holder), so requires no fixings.
Main scale in centigrade, with smaller markings in Fahrenheit.
It mounts on the exterior of a window to monitor conditions outside. They have large digits that can be read from right across the room, but are printed on clear vinyl backgrounds to minimise their intrusion on the view. Both have their main temperature scales in centigrade with the smaller markings in Fahrenhit.