# Fermi numbers > About 40 seconds after the explosion the air blast reached me. > I tried to estimate its strength by dropping from about six feet small pieces of paper before, during, and after the passage of the blast wave. > Since, at the time, there was no wind I could observe very distinctly and actually measure the displacement of the pieces of paper that were in the process of falling while the blast was passing. > The shift was about 2 1/2 meters, which, at the time, I estimated to correspond to the blast that would be produced by 10,000 tons of TNT. > > — _Enrico Fermi, [Top Secret interview](http://www.dannen.com/decision/fermi.html?utm_source=longform.asmartbear.com&utm_campaign=longform.asmartbear.com&utm_medium=post) July 16, 1945, declassified in 1965_, output blast was 21K tons of TNT - No ranges - only powers of 10: 0.1, 1, 10, ... 100000, 1M... ## Reference - [Fermi ROI: Fixing the ROI rubric](https://longform.asmartbear.com/roi-rubric/) ## Avoid wishy-washy estimation words - \[un\]likely - probably - few - many - almost always/never [source](https://longform.asmartbear.com/probability-words/) | Probability Word | Probability Value | Expected Range | | -------------------- | ----------------- | -------------- | | Certain | 100% | 100% | | Almost Certain | 93% | 87% … 99% | | Probable | 75% | 63% … 87% | | Chances About Even | 50% | 40% … 60% | | Probably Not | 30% | 20% … 40% | | Almost Certainly Not | 7% | 2% … 12% | | Impossible | 0% | 0% |