The present invention relates to a method for calculating or estimating or approximating one or more values representing parameters of a patient, the method comprising the step of interpolating or extrapolating of at least one later value of a first parameter taking into account at least one earlier value of the first parameter, at least one earlier and at least one later value of a second parameter, and a mathematical relation between the first and the second parameter. It further relates to an apparatus, a blood treatment device, further to digital storage means, a computer program product, and a computer program.
