Abstract: Sensor member having on it a ceramic crystal, is secured to a sieve or sieve frame of a combine harvester to be shaken with the sieve or sieve frame being so located that any grain which is discharged from the sieve and otherwise wasted will impact upon the sensor and cause an electrical signal to be transmitted by the crystal, the signal being amplified and transmitted to a readout station which enables the operator to immediately identify when grain is wasted. In being shaken along with the sieve the sensor presents a clean face to the grain, which might otherwise be partly obscured by chaff or other discrete material and this results in a higher degree of accuracy in the determination of wasted grain.