Well, the change in f is the value of f at the upper point here, which is x0+delta x, and minus its value at the lower point P, which is f of x0, divided by delta x.
Since the rate of change (illustrated by the positioning of the balance point in the figure) was lower, more anticipatory designing versus refactoring may have been reasonable.
由于变化的速度慢(图中由天平的支点比较靠左来表示)，早期的预测多一些是合理的。
3
The ceiling system should satisfy these requirements that using lower chord ball as fixed point, adapting space change of hyperboloid steel grid, grid settlement under snow load.