EER, ESEER, SEPR, PUE - key figures in the data center industry should help TGA planners, data center operators or engineers to better assess the efficiency of a data center. However, caution is required here, as the key figures are partly based on values that allow only a moderately realistic assessment. To shed some light on this topic, we interviewed our product manager Tobias Wolf. He analyses the individual characteristic values, the underlying formulas and gives helpful tips on how the values can be interpreted.