AI Tool said the tank would take about 6.1 hours to heat, right down to one decimal place. That precision can be deceiving — a very specific-sounding number feels trustworthy, but precise isn't the same as correct. To do the calculation at all, the model needed a starting water temperature, and nobody in the conversation had given it one. Rather than asking, it quietly picked a typical value and used it as if it were a fact you'd supplied. The arithmetic that followed is completely correct — the problem is one step earlier, in what it assumed going in without telling you.