Abstract: An apparatus end method of validating coins involves taking two independent measurements of the tested item, and determining whether both measurements lie within respective ranges for a particular coin type, the range for at least one of the measurements being dependent upon at least one other measurement.

Abstract: A coin validator has a thickness sensor formed by two coils positioned one on each side of the coin path. The coil outputs are processed separately to derive values which, when combined, produce a thickness-indicating measurement which is independent of coin position. Each output may be processed to give values which are linearly dependent upon coin position with the same constant of proportionality. Alternatively, one output is scaled relative to the other to an extent dependent upon the thickness for which the coin is to be tested, so that the thickness-indicating measurement does not vary significantly over a region which corresponds to a likely maximum variation in the position of coins of that thickness.

Abstract: Target pixel signals representing radar echo signals are stored in an addressable memory; and the contents of at least selected storage locations within a preset guard zone are read out of the memory. If a pixel signal of sufficient value is stored in the read out location, the presence of a target within the preset guard zone is indicated if that pixel signal is verified as being one of several which, presumably, are derived from a target.