Although the average was zero, each interval had a maximum (and a minimum) reading. In this graph, my APM is displaying a flat zero line indicating the average but also the maximum value.
虽然平均值是零，但是每一个时间间隔都有一个最大(和最小)读数。
2
Say you have a minimum, well, the tangent plane at this point, at the bottom of the graph is going to be horizontal.
如果你说这是个极小值，那么这点的切平面应该是水平的。
3
Though examples of common signal and sine signal, by the frequency spectrum graph and theoretical analysis, the minimum sample rate of the sampling theorem is made clear.