Various embodiments include a method for operating an internal combustion engine wherein the compression is variably adjusted comprising: checking a sensor signal indicative of a compression of the engine; checking the plausibility of the signal by: ascertaining a series of corresponding values of the signal and values of the actuating variable; determining a mathematical relationship between the signal and the variable based on the series; determining a deviation between the relationship and a predetermined characteristic relationship; and determining the signal is plausible when the determined deviation is lower than a predetermined threshold value; and if the determined deviation is higher than the predetermined threshold value, adjusting operation of the internal combustion engine.