No similar ratios of relative cost have been estimated in regard to the various classes of packets other than parcels, since they are dealt with together, and it is necessary, therefore, to ascertain the actual cost for staff under the various headings of collection, stamping, sorting, and delivery. As regards collection, it is difficult to discover a basis on which a computation of the relative cost for the different classes of packets may be made, because the cost varies greatly, not only as between each class, but from place to place, in regard to any particular class of packet. Many of the ordinary letter packets are posted in large numbers at head post offices, and in respect of packets so posted there is no cost of collection. Light letter packets and halfpenny packets (especially halfpenny packets) are, moreover, handed in at post offices in considerable numbers for prepayment of postage in cash. In that case the cost of subsequent handling is slightly reduced, because under the regulations for such prepayment the packets must be tied in bundles with the addresses in the same direction, that is to say, the operation of facing must be performed by the person who posts the packets. Against this, however, must be set the very considerable expense incurred both in towns and rural areas for the collection of ordinary light letter packets, postcards, halfpenny packets, and newspaper packets from posting boxes, and the cost of van services, which are frequently provided for the collection of letters from business premises. Very little of the cost of these services can be attributed to the heavier letter packets, which are to a large extent handed in at the post office counter to be weighed. This involves considerable expense, which corresponds to cost of collection, and may be dealt with under that heading. The best estimate that can be made is that the cost of collection per packet is approximately the same in all cases. Facing and stamping may be regarded as one operation, the one being really preparatory to the other. Here there is less difficulty. The relative cost per packet may fairly be taken as the ratio of the time taken in performing the operation in the case of each class of packet. In regard to facing and stamping, and also in regard to sorting, the letter packets proper, that is to say packets sent at the ordinary letter rate of postage, fall in general into three classes according to the facility with which they can be handled, viz. (1) "short letters," (2) "long letters," (3) "letter packets" (that is, the bulky packets sent at the letter rate).[620] In order to complete the calculation, the number of packets which fall respectively into these three classes must be estimated.