The products most traded in on the Board of Trade are wheat, corn and oats, and to a lesser extent the cured hog products, rib sides, lard, and mess pork. The smallest units traded in are 5,000 bushels of grain and 50,000 pounds of provisions. In the case of the grains, the contracts most commonly traded in are contracts for delivery in December, May, July and September. In the case of the pork products, the contracts most traded in are contracts for delivery in January, May, July and September. Before the war, trading in December corn customarily opened in the month of May. The price of December corn as quoted in May was necessarily based on the supposition that the ensuing crop would be a normal crop, neither greater nor less than the average. If there was cold, wet weather in May or June, the price advanced. If the weather was warm and rather dry, the price declined slightly. However, as a general proposition, before the war, the price held practically steady during the months of May and June. During July and August, however, corn values on the Chicago market oscillated back and forth with rainfall and drouth, registering the changes in marvelously delicate fashion. Customarily, before the war, it took an average rainfall, in the seven great corn states, of about one and a quarter inches during ten days, to hold the price of December corn futures practically stationary. A rainfall of as much as one and three-quarters inches in a ten-day period during July and August would ordinarily depress the price by several cents a bushel, whereas a ten-day period with no rainfall at all would customarily advance the price by eight or nine cents a bushel or even more if the temperature was high. Anyone who studies these things is surprised at the accuracy with which the market price before the war actually reflected crop conditions as they changed from day to day. Since the war, it has been more difficult to measure the price-making forces. Political conditions in Europe even during the months of July and August often have had as much influence as the weather in determining the price of corn.