21.—(1) Every non-automatic weighing machine which is in use for trade for operation by a prospective buyer for the purpose of making known to him the weight and where appropriate the price of goods selected by him shall—
(a)be a self indicating weighing machine; and
(b)be specified as being for such use in the published particulars of the approved pattern in the case of a weighing machine having a digital indicating device.
(2) In addition, any machine which is made available as a self service weighing machine shall—
(a)be a price computing weighing machine having digital displays of weight, unit price and price to pay, together with an associated label printer;
(b)have any bag provided for the goods selected by the prospective buyer such that the goods are readily visible through it; and
(c)only be used in connection with the sale of different commodities, other than commodities having the same unit price, provided that they are readily distinguishable from each other.