Quantum Fermi Estimates. How many piano tuners are in your lunch box?
First, express in scientific notation, 0.0 x 10^0, multiply this by all likely relevant factors (how many pianos can you tune in a day, did you eat that sandwich and free up some space), multiply, fix the units, and then establish some confidence intervals.
And... it's about 0. Pretty remarkably close given I didn't collect any real data.