And then again there are all the possibilities of the printer's art to be used, in connection with the preparation of elaborate tariffs.[176] The tariff of "33 cents per hundredweight" may conceivably be a typographical error, to be speedily corrected in a supplementary hektograph sheet filed the next day. Involved and elaborate rate sheets may be reprinted with only one little change among a thousand items left as before. Different tariffs may interlock with complicated cross references. In one case in 1902 it took seven different tariffs to enable one to compute the rate for a given shipment. In twelve months, to December 1907, there were filed with the Interstate Commerce Commission 220,982 such tariffs, each containing changes in rates or rules. Some "expire with this shipment,"--and some agree to "protect" any rate of any competing carrier, that is to say, to meet it if it happen to be lower. An entirely different plan of rebating,--and a most effective one,--has to do with apparently unrelated commercial transactions.[177] Many shippers are large sellers of supplies to the railroad. How easy then to make a concession in rates to an oil refinery for example, by paying a little extra for the lubricating oil bought from a subsidiary concern. The Federal authorities in recent years and especially in connection with the prosecution of the Standard Oil Company in 1908-1911, have discovered the most extraordinary variations in the prices paid by railroads for supplies. Independent concerns were often not allowed to compete in the sale of lubricants at all. It would be difficult to prove any connection between so widely separate sets of dealings; and yet it is clear that rebates are often given in this way. Or even more fruitful as an expedient, especially in these later days when rebating is a serious offence, why not confer a favor by extra liberality in allowances for damages to goods in transit? In 1909 the so-called Beef Trust was specifically ordered by the Attorney General of the United States to desist from such practices. Positively the only way to detect such fictitious allowances for damages, is to ferret out each case by itself. This is a slow and necessarily expensive process. Damage allowances and _quid pro quo_ transactions in the purchase of supplies, are indeed almost "smokeless rebates," as they have aptly been termed.