Check units before calculating

Equal numbers can describe different quantities when units differ. Confusing centimeters with meters, pascals with kilopascals, or 0.05 with 5% can change a result dramatically.

Rounding intermediate values can accumulate error. Retain precision during calculation and round the final display where possible. Displayed significant digits should not imply more certainty than the measurements support.

Direct unit conversion requires matching dimensions. Converting volume to mass needs density, and pixels to inches needs pixel density. Do not silently assume a material property that was not supplied.