Evaluating method and apparatus for a test voltage by use of a bandwidth-limited evaluation circuits. For evaluation of a measured signal dependent on a variable parameter, an identification is first undertaken with a broad-band evaluation circuit to determine whether an interesting sub-region of the overall variation region of the parameter has been reached. When this is the case, then a reduction of the bandwidth of the evaluation circuit and a reduction of the variation rate of the parameter occurs in order to be able to evaluate with high sensitivity in the interesting sub-region.