The last class is illustrated in the manufacture of salt. The brine──raw material──is pumped from the wells into storage tanks, from which it is drawn into evaporating pans or grainers. An order may be issued to make what is known as _common fine salt_ in three of these evaporators. Evaporating processes are influenced by atmospheric conditions──the same heat will evaporate the brine much more rapidly one day than another. Also, the brine is of different degrees of strength──the same quantity does not always contain the same amount of salt. The only definite factor is time──an indefinite quantity of brine is converted, in a given time, into an indefinite quantity of salt and, it might be added, of an indefinite quality. When all these conditions are considered, together with the fact that each manufacturer has his individual methods of conducting the business──methods probably different from those of his competitors in the same line──it will be seen that the variety of forms of production orders is almost without number. But the important thing is to have an order of some kind──to provide a record. If there is one essential feature to be incorporated in the production order, it can be expressed in two words──definite instructions. The order should be made perfectly clear, leaving no room for doubt, as to what is desired. When No. 3 dining─room chairs are wanted, the order should state the fact very clearly, and not read _chairs_, leaving the superintendent to guess the style and size. [Illustration: Fig. 39. Production Order to Superintendent] [Illustration: Fig. 40. Production Order Which is an Exact Copy of the Customer's Order] The form of the production order need not be complicated; indeed, a simple form will serve the purpose much better, an illustration of which is shown in Fig. 39. The heading of this order shows the number and date, with instructions to the superintendent to carry out the work as specified. The body of the order is blank, providing space for entering such details as may be necessary. The blank at the bottom, which is filled in by the superintendent's clerk, shows the date received, date started, the shop order number, and the date finished. [Illustration: Fig. 41. Sub─production or Shop Order] This form is suitable for almost any kind of business or class of order. The production order should always be made in duplicate, a copy to be kept in the office. The office copy will be used to follow up the manufacturing order.