The Prussian rates of 1712 continued in force until 1762, when a general revision of postal rates was necessitated by the financial difficulties resulting from the outbreak of the Seven Years' War. The rates for ordinary commercial transport in Prussia rose to such a degree that the post, still working on rates fixed in 1712, became the cheapest means of transport. Consequently the parcel post traffic increased, but it was found that the expenses of the service were not covered by the revenue derived from the parcels. The rates were accordingly increased on the simple plan of raising them all by 100 per cent. (except in Ostfriesland, where the increase was 50 per cent.). A further revision of the rates was made in 1766. Apart from the fact that the rates were further increased, this revision was in many respects beneficial, since it introduced a uniform and definite rate for the whole country.[440] In 1770 the rates of 1712 were restored. Up to this time the rates had been based partly on the actual length of the post routes, partly on the time occupied by the post-messengers in traversing the routes. They therefore varied according as the roads were good or bad.[441] In 1801 a mathematical measurement of the roads of Prussia was made, and thereafter the time factor was eliminated and the rates based on distance only. The distance was measured, not in a direct line, but by way of the post routes. The events of the Napoleonic period resulted in a great increase of prices in Prussia, and in order to meet the additional expense of conducting the posts, the rates were increased by 50 per cent. between 1805 and 1811, but the general basis of charge remained unchanged. In 1824 important modifications were introduced. The discrimination according to the nature of contents of parcels was abolished, and the rates were based solely on considerations of weight and distance of transmission. Further, the distance between post offices was no longer to be reckoned according to the distance by way of the post routes, but according to the direct distance.[442] The general parcel rate was fixed at 3 pf. per pound for each 5 miles, with a minimum charge of twice letter rate for parcels not exceeding 4 pounds in weight, and three times letter rate for parcels weighing more than 4 pounds. In the case of several parcels directed to the same place, the postage was reckoned according to the total weight. The Postmaster-General was authorized to increase the rates in the event of a rise in the cost of forage.[443] A special rate, in addition to ordinary postage, was also introduced in respect of parcels directed to or sent from offices for which no normal rate had been fixed. In 1826 a reduction of postage by 10 per cent. was authorized where the total yearly weight of parcels was between 10,000 and 20,000 pounds, and of 15 per cent. where the total yearly weight exceeded 20,000 pounds. This reduction was, however, abolished in 1848.