=Unbalanced Bids.= We shall assume again, for purposes of illustration, that a certain contractor desires to bid on some public work involving the removal of 100,000 cubic yards of earthwork and 50,000 cubic yards of rock work. He estimates that he can do the earthwork at a profit for 30 cents per cubic yard, or $30,000; and rock work for 80 cents per cubic yard, or $40,000. If the work in the above example were _classified_, and the contractor were paid so much money for each yard of rock and so much money for each yard of earth excavated, and his bid read 80 cents for rock and 30 cents for earth, it would be said to be a _balanced bid_. Other contractors, seeing his bid, would know that he considered that he could do the rock work at a profit at 80 cents, and earthwork at a profit at 30 cents. In order to prevent them from obtaining this information, the contractor can _unbalance_ his bid, as it is termed; and in this event he would bid perhaps as follows──namely, 100,000 yards of earth at 40 cents, or $40,000; and 50,000 yards of rock at 60 cents, or $30,000. The total amount of this contract would be the same, and he would make the same profit; but his competitors would be deceived as to his basis of doing work. The disadvantage of this from the contractor's point of view is that, in the event of an error having been made in an estimate of quantity, he might find himself doing less than 100,000 yards of earth and more than 50,000 yards of rock, in which event he would stand to lose money. =Material Supply.= In concrete work particularly, it is all─important that material──cement, sand, and stone──be promptly shipped, and at the same time not too promptly shipped. If the shipments are not promptly made, there will be a failure of material to arrive, which will throw the men out of work, with all that this implies in high costs. If the material is shipped too rapidly, it will be necessary either to unload it into a stock pile, which will involve the re─handling of the material; or to pay demurrage charges to the railroad company, if the shipments are made by rail. In such work, at a time when there is likely to be any freight congestion in the country, stock─pile facilities should be provided to care for a supply of material to carry the work for one to two weeks.