The equal tax law ("junshuifa"), also known as the square field law ("fangtianfa") was a land registration project meant to reveal hidden land (untaxed land). Fields were divided into squares 1,000 paces in length on each side. The corners of the fields were marked by earth piles or trees. In the autumn, an official was dispatched to supervise the surveying of the land and to place the soil quality in one of five categories. This information was written in a ledger declared legally binding for the purposes of sale and purchase, and the taxation value assessed appropriately. The law was highly unpopular with land owners, who complained that it restricted their freedom of distribution and other purposes (avoiding tax). Although the square field system was only implemented around the region of Kaifeng, the land surveyed made up 54 percent of known arable land in the Song dynasty. The project was discontinued in 1085. Emperor Huizong of Song (r. 1100-1125) tried to revive it but the implementation was too impractical and gave up after 1120.