Percentage calculation
The three most common questions, each with its own input row — change whichever you need.
① What percentage of B is A
② Increase / decrease A by P%
③ Change rate from original value A → current value B
Watch out for negative numbers and zero
Growth rate has no intuitive meaning when the original value is negative (−100 to −50: up or down?). This is marked as not applicable instead of giving a misleading number.