I am new to fitting histograms and as a result i have an issue understanding what to consider as error propagation when calculating a quantity. The following diagram shows entries for 4 different x-ray sources resulting in for different data files generating 4 histograms which are fitted separately. Lets say i want to calculate the quantity u= a*channel for the Rb source (check the following diagram). If i wanted to calculate an error propagation as well based on the results of the fit model what should i consider as error for the Rb channel value. Should i use the ±\pm values? or the sigma value or both? The well known error propagation formula is the following: σu2=(∂u∂(channel))2σchannel2σ^2_u = \left( \frac{\partial u}{\partial (channel)} \right)^2 σ^2_{channel} Is this formula too simplistic for this? Can i apply it here? P.S. First 3 values on every pad refer to the histogram. We are interested in lines 4-7 which refer to the fit. P.S.2 The diagram is generated using CERN root framework.