In IC^2 there's at least 2 machines that i know of that have the value of heat and their operation depends on heat. Nuclear reactors may explode at high heat and both reactors and induction furnace smelt/breed uranium faster at high heat.
i think there needs to be a tool to measure the temperature of these two machines.
Thermometer Recipe:
_ I _
_ E _
_ * _
I - refined iron
* - redstone dust
E - electronic circuit
_ - nothing
Suggestion 2 - have an indicator of heat in GUI of these machines, which would make more sense because having a separate tool just to use with 2 machines would be a little pointless.