1. The problem statement, all variables and given/known data Say we have the equation D2 = C x N where C = A2. Using a graphical method to find the % uncertainty of C (from graph of D2 against N) which involves working out the gradient which equals C and so forth. This value is 25%. The question is "what is the percentage uncertainty of A?" This is actually a question that appeared in an A-level paper i did today and it was the only one that really bamboozled me . 2. Relevant equations 3. The attempt at a solution I realize you don't divide by two;my reasoning being that when asked to calculate the % uncertainty of r in say the equation V = 4/3 x π x r3 the question doesnt explicitly state r3. So i think that it is between doubling 25% or just leaving it. Now i think it was the latter but in the exam I did indeed double it to 50%.