Rounding a Calculation

Enter two measured values, choose an operation, and press Run. The steps appear one at a time: each value and how many digits it carries, the operation, the rule that applies, the raw answer, and the answer rounded correctly — because a result can never be more precise than the measurements it came from.

Type values with different numbers of digits Switch between × ÷ + − Press Run to walk through it step by step

The two rules

Multiply or divide: the answer keeps as many significant figures as the input with the fewest.

Add or subtract: the answer keeps as many decimal places as the input with the fewest. Here it is decimal places that matter, not significant figures.

The idea behind it

A measurement carries uncertainty in its last digit. When you combine measurements, that uncertainty carries through — so the answer cannot be sharper than its roughest input. Rounding to the right place is how you stop the calculator from reporting precision that was never measured.