… I asked the question that is always uppermost in the mind of an engineer. With respect to the amount of fissionable material needed for each bomb, how accurate did they think their estimate was? I expected a reply of “within twenty five or fifty percent,” and would have not been greatly surprised at an even greater percentage, but I was horrified when they quite blandly replied that they thought it was correct within a factor of ten. … after extensive discussion of this point, I concluded that it simply was not possible to arrive at a more precise answer.