Bar for temperatue don't work fine

hi, i have create a face with 3 bars.

the center one is for the battery watch.

the right one is for humidity and work well,
because humidity go from 0 to 100.

the left bar is for temperature, but like you see
at the bottom i have placed -10°C, while on the
top is +40°C.
in Fahrenheit they are about 14-104°.
of course the 0 is not at the bottom, because here
is -10, and for this i don’t know what to write inside
fill ratio for have the right temperatures.
someone can help me with this ???
thank you very much.