An encoder to be mounted to a shaft extending from a piston meter configured to compute a volume of distributed fluid includes a magnet affixed to the shaft via a floating magnet holder, a magnetic sensor configured to sense the flux density and direction of a magnetic field created by the magnet and to output a signal indicating the flux density and direction of the magnetic field to a printed circuit board, and the printed circuit board configured to output a signal indicating the volume of distributed fluid if the encoder has not been tampered with and configured to output an error signal if the encoder has been tampered with.