Here’s the situation: For temperatures less than 0 °C an industrial platinum resistance thermometer can be characterized as follows:

AT[sup]4[/sup] + BT[sup]3[/sup] + CT[sup]2[/sup] + DT + E = R

Where T is the temperature (°C) and R is the resistance (ohms). A, B, C, D, and E are known coefficients.

This equation is (obviously) wonderful for computing R if you already know T. But it’s useless when you measure R and try to compute T (which is what we do).

Up until now I have relied on Excel’s “solver” tool, but I find it annoying and risky because the user has to manually *invoke* it. I would really like to derive an inverse equation so Excel can do it “on the fly.”

Any help would be appreciated. Thanks.