An electronic device having a circuit board, a shielding plate disposed thereon and a three-terminal regulator is provided with a heat sink positioned on the outer side of the circuit board and connected to the three-terminal regulator. A signal processing apparatus for performing, when a region to be subjected to signal processing has shifted, signal processing of pixel signals in a region to be subjected to signal processing after shifting the region, by utilizing old pixel signals already subjected to signal processing before the shift of the region. An optical unit is mounted on the measuring piece, for receiving at least one test-piece beam, interacting with the reference structure on the test piece, running essentially in a measuring plane.