Mark Levi notes an interesting coincidence in his book Why Cats Land on Their Feet: And 76 Other Physical Paradoxes and Puzzles1 (2012).
Dividing normal body temperature (expressed in degrees Celsius) into 100 approximates $$e$$: \[\frac{100}{36.8°} \approx e = 2.718281828459045\ldots\] Levi writes:
The estimate will be on the low side if you run a fever, or on the high side if you have hypothermia. This observation makes the natural logarithm — the one with the base $$e$$ — seem even more natural.
A floating point number $$B$$ that expresses the body temperature of a person (expressed in degrees Celsius).
The sentence you have a fever if the approximation $$\frac{100}{B}$$ is less than $$e - 0.1$$.
The sentence you have hypothermia if the approximation $$\frac{100}{B}$$ is greater than $$e + 0.1$$.
The sentence you have a normal body temperature if the approximation $$\frac{100}{B}$$ falls inside the interval $$[e - 0.1, e + 0.1]$$.
Input:
32.1
Output:
you have hypothermia
Input:
37.8
Output:
you have a normal body temperature
Input:
42.6
Output:
you have a fever