Measurements Mathematics and 1 Calculations with Sig Digs Rules for Adding and Subtracting Measured data must be the same kind of dimension and have the same units before they can be added or subtracted. The sum or difference of measured data cannot have greater precision than the least precise quantity in the sum or difference. Rules for Adding and Subtracting = 23.8 cm 23.80 cm 2.1 cm 21.70 cm + 262,729.12 = 263,000 259,000 3,729 0.12 + Rules for Multiplication and Division The product or quotient of measured data cannot have more SDs than the quantity with the fewest SDs. The product or quotient of a measurement and a counted number, conversion factor, or defined value has the same number of decimal places, or the same precision, as the original measurement.