I dont understand how to calculate percentage uncertainty!? I know in chem we calculate uncertainties by smallest division/the reading X 100. But in physics i am clueless. For instance heres an example The power loss P in a resistor is calculated using the formula P = V^2/R. The uncertainty in the potential difference V is 3% and the uncertainty in the resistance R is 2%. What is the uncertainty in P? (this is not homework) I just want to know how to get sums like these.