thus the derived barcode sensed threshold value t bs will be an optimal value for the remaining items 7 in another particular embodiment the barcode sensed threshold value t bs can be derived from the output signals s from ones of the previous items 7 thereby representing a best fit value for example an average value where items 7 of a certain kind are routinely utilized the derived barcode sensed threshold value t bs will be an optimal value for the items 7 which are routinely used in one embodiment particularly where relatively large batches of items 7 are handled at a time the barcode sensed threshold value t bs can ordinarily be a first derived value typically a best fit value but where a predetermined number of items 7 having the same reflectance and hence substantially the same barcode sensed value s bs are successively handled the barcode sensed threshold value t bs can instead be derived from the output signal s from at least ones of the predetermined number of items 7 in another embodiment particularly where the optical sensor 1 is utilized to actuate another device for example a printing device downstream of the optical sensor 1 and thereby with a time delay relative to the leading edge of the item 7 passing the detection location l the barcode sensed threshold value t bs can be derived from the captured output signal s from the receiver element 5 the barcode sensed threshold value t bs is derived from one or both of the barcode sensed value s bs and the barcode background value s bb in being determined from an output signal s from.