A square wave can be decomposed into odd sine harmonics. Their amplitudes are : higher frequencies contribute less. Adding the seven terms shown approximates the square wave.方波可以分解为奇次正弦谐波，各项振幅为 ，频率越高，振幅越小。将图中的七项相加，就得到方波的近似。
Vector rotates at angular speed , with length . Connecting the vectors adds their vertical projections: the tip traces the wave, and the bars show amplitudes.第 根向量以角速度 旋转，长度为 。首尾相接后，末端高度就是各竖直投影之和，描出波形；柱形高度表示振幅。