I have tried finding a table's length using two methods. Both should be applicable, as using a ruler implies uniform distribution, does it not? The first method involved calculating the mean length from a set of measurements, finding the variance, and substituting it in the formula for the total uncertainty, namely sqrt((variance/N) + (ruler's resolution)^2). The second method involved using the formulae for uniform distribution to find the mean and deviation. The results were different. I am 100% certain the first method is correct. But why would the uniform distribution formulae not be applicable in this case?