With every result produced by a laboratory there is an associated uncertainty, which may be attributed to a number of small variations arising at any stage of the analytical process, from sample collection to analysis. It is important to understand that uncertainty is not the same as an error. An error implies that there is a difference between a measured value and the true value caused by an unknown factor, whereas uncertainty is an acceptable interval within which a result can fall. We are able to predict this interval by calculating the measurement uncertainty (MU) for tests within our repertoire.