How is value for "Original Temperature" determined?

+1 to @afre’s call for ‘simple’.

I found the color temperature thing to be unhelpful; I didn’t start to get good white balance until I used the patch/dropper method. Later, I learned to recognize out-of-alignment channels and to adjust white balance manually with per-channel curves.

Simply, white balance is about making white have identical values for the red, green, and blue channels. I think adjusting color temperature assumes your imbalance is mostly in the simple
spectral difference between what the camera asserts and the actual temperature, but a lot of light these days doesn’t cooperate with that assumption.

I just wrote a whitebalance tool for rawproc, and I skipped the whole color temperature thing…