1. The problem statement, all variables and given/known data Compute the moment of intertia Io of the two cylinders, per their axis of symmetry, and then, using Steiner's formula, the moment of inertia Ib, as per the axis of rotation. 2. Relevant equations Io = 1/2*m*R2 Ib = 2*(Io + m*x2) 3. The attempt at a solution Now, this is one of those huge exercises that you do at the Lab, which give you hours 3, plus work at home. So, this is just a part of it, but I'll type down what I've found already. See, the problem here is computing the error. The formula for an f(x,y,z) fraction, is: δf = √[(∂f/∂x*δx)2 + (∂f/∂y*δy)2+ (∂f/∂z*δz)2] So far so good, right? From the previous questions, I have (relevant to this exercise): R +- δR = (2,10000 +- 0,00025)*10-2 m x +- δx = (5,00000 +- 0.00025)*10-2 m m +- δm = (435,150 +- 0.005)*10-3 kg Io +- δIo = (9,595 +- 0.002)*10-5 kgm2 Plus, from the above formula: Ib = 2,36690115 * 10-3 kgm2 From our professor, we know Io should be in the range of 10-5 and Ib in the rang of 10-3, so that's all good. The problem I'm facing is when I try to find the error of Ib. First of, I'm not sure if I should break down Io into Io = 1/2*m*R2 and have x = m, y = R & z = x (going back to the general error transmission formula). At first I tried this, and then the next time I kept it as is, and went x = m, y = Io & z = x. Still, the problem persists. See, the SI units don't add up when I do the partial derivatives, apart from ∂Ib/∂m. And so, I can't add up the results of each derivation, and put them into the square root to get a result of [...] kgm2. So, what do I do now? In later questions, wehen we have to compute something else, certain of its quantities, we are instructed to use without their errors, as simple constants. Any help is appreciated!