A portable electronic device is provided with a storage section which stores various pieces of information and a transmitterreceiver section which transmits and receives data to and from external equipment. A first fibre mat is laid onto an inner surface of a mould. The refractometer comprises a sample stage arranged surrounding the interface surface. Although the component parts are min is the spray gun is capable of flowing coating mixture at the same rate as the larger version convergent spray gun. Error correction includes i) detection of each systematic error, ii) feedback of the systematic error to circuitry within the memory, and iii) subsequent adjustment within that circuitry to cause a correction of systematic error in the output signal of the multi-level flash memory.