You can use a level on top an 8 ft.-long 2×4 to determine the slope for yard and garden projects. If you need a slope of 1/4 in. per foot, tack a 2-in. block under the 2×4 on the down- slope end. When the bubble is level, you will have 1/4 in. per foot (2 in. divided by 8 ft.). You can vary the block height for other slopes. If you want a slope of 1/2 in. per foot, make the block 4 in. high.