Here is what seems to have happened: Note that whenever the answer is not accurate, Google uses scientific notation. For example, 1e15 + 30 = 1.0 × 10^15. We ac

Here is what seems to have happened: Note that whenever the answer is not accurate, Google uses scientific notation. For example, 1e15 + 30 = 1.0 × 10^15. We accept this as true because Google only claims it is true to two sig figs. However, in this case, Google means to say 0.0 × 10^15, indicating two sig figs of accuracy. Google's mistake is probably that the internal notation used does not allow it to distinguish between "0" and "0.0 x 10^15", and so it does not report that the result is only accurate to two sig figs as it should. So, if Google somehow reports the "zero" result in scientific notation with two sig figs, then it will be consistent with the rest of their calculator and clear that it may not be an accurate result.