Spin-rate distributions of the 20-min cadence surveys. The spin-rate distributions for asteroids of \(3< D < 15\) km (upper) and \(D < 3\) km (lower) at inner (left), middle (center), and outer (right) main belt. The solid black line and blue dashed line are the original and de-biased results, respectively. The number of asteroids used in each distribution is indicated in each plot. Note that the number of asteroids of \(D > 15\) km and that of \(D < 3\) km in outer main belt are too small to carry out meaningful statistics.