Correct energy measurement is vital for electric energy trading. There are often stringent legal demands on the revenue metering that require periodic in situ substation verification. Traditional energy metering testing methods are not possible in IEC 61850 digital stations using a process bus. In this article we will show that it is possible to use data analysis to verify the accuracy of energy measurement systems in substations. Our algorithms can be used as a part of the legal verification and runs remotely on-line. As a consequence, some of the periodic accuracy verification including substation visits can be abandoned. The on-line algorithms makes it possible to decrease the errors in both revenue metering systems and in other energy measurements systems in the Swedish transmission system. Measurement errors are now detected and amended much faster which reduces incorrect billing. The estimated value of incorrect billing is decreased by more than a million EUR annually. Our algorithms also provide a solution to bridge the problem to verify measurements in future fully digital substations.