The superman penny shaving attack is not related to rounding behavior. You may multiply with fractional values, but when you add or subtract from a ledger, you

The superman penny shaving attack is not related to rounding behavior. You may multiply with fractional values, but when you add or subtract from a ledger, you are doing so in fixed precision (usually cents). If you were calculating something like interest and consistently rounding in one direction, you'd be either over or undercharging people, but the money wouldn't vanish. In other cases, you need to actually think about rounding mode (e.g. how many shares of AAPL can I buy with $5000). > there's no problem statement on his entire website to address what actual problem he was trying to solve This is very true. I don't understand what problem this is trying to solve, because I don't spend a lot of time confused by the internal detail that a double is binary. The storage format isn't important beyond knowing roughly how many digits of accuracy I can count on.