Describes a series of routine self-checks that the Uppsala carbon-14 laboratory performs with all measurements; all uncertainties in the physical measurement of a sample are estimated. The laboratory studies long-term stability, calculates mean values for oxalic acid and background, and compares expected and real statistical distributions of uncertainties. To reduce the risk of bias, the samples from each series are almost always run on the same counter. Some samples are, however, run on two or more counters to check the possible bias to achieve reliable activity comparisons with other laboratories. It is always possible to trace which counter is used, since different number series are used for different counters.