  We introduce an experimental procedure for the detection of quantum
entanglement of an unknown quantum state with as few measurements as possible.
The method requires neither a priori knowledge of the state nor a shared
reference frame between the observers. The scheme starts with local
measurements, possibly supplemented with suitable filtering, that can be
regarded as calibration. Consecutive correlation measurements enable detection
of the entanglement of the state. We utilize the fact that the calibration
stage essentially establishes the Schmidt decomposition for pure states.
Alternatively we develop a decision tree which reveals entanglement within few
steps. These methods are illustrated and verified experimentally for various
two-qubit entangled states.
