Hydraulic elevators have to track exactly the same velocity pattern, in spite of changing operating conditions and varying friction effects. For cost reasons very few online measurements are possible and, in particular, a continuous measurement of the target quantities (in particular, the acceleration of the cabin) is not available. So the tracking control must be based to a very large extent on an adaptive feedforward part. To allow this, an extension of the measurement space is proposed, which allows to strongly improve the performance while keeping the system complexity and costs very low. This paper deals with the design of such a measurement extension, in particular with the design of a novel displacement measurement system used for estimation of the flow of hydraulic oil.