When learning positions for drill, an American football field may be divided into a 5-yard grid, with the yard lines serving as one set of guides. The locations where the perpendicular grid lines cross the yard lines sometimes called "zero points" or gacks, may be marked on a practice field at eight-, four-, or two-step intervals. Alternately, band members may only use field markings—yard lines, the centerline, hash marks, and yard numbers—as guides (but note that different leagues put these markings in different places).