A plough is pulled across the field and cuts a rectangular furrow slice with two knives, the share and the coulter. The furrow slice is then flipped over by the wrest or mouldboard to make a furrow.
With a fixed wrest the furrow always fell in one direction. If you went up the field and then back again the furrows rested as shown in the sketch above.
In Kent, mainly due to the heavy soil and rolling landscape, a turnwrest plough was used. In simple terms, the wrest could be taken off and put on the other side of the plough when coming back across the field.
With this method of ploughing all the furrow slices rested on top of each other. When ploughing on the side of a hill all the furrow slices could point uphill thereby helping to prevent erosion.
A development of the turnwrest plough was the balance, one way or cock up plough. This had two shares, coulters and mouldboards arranged so that only one was used at a time, the other being up in the air. After one furrow had been cut the tow bar is swung over to bring the part which had been up in the air down to the ground and the second furrow was then cut. The second mouldboard threw the new furrow in the same direction as the first, so that each furrow rested on top of the previous one.