This paper would provide the analyst with an easy to use step-by-step guide to calculate the uncertainty of measurement in implementing a new analytical method. There are two main ways to attain such an achievement. The first is to consider all the possible sources of variability and then to sum up all of them in the final calculation. The second is taking part in a collaborative trial and processing the resulting statistics. Both methods imply different advantages and drawbacks. It is up the analyst to choose the one fits best his requirements. Anyway it is nearly inescapable providing, along with the test result, its own uncertainty.