When there is a change in price, there are two effects: one is stability, which is the section space where the second derivative is greater than zero. In this section space, the movement of prices is accompanied by resistance from hidden buy or sell orders. The other effect is instability, which is the section space where the second derivative is less than zero. In this section space, the effect is the panic emotions generated by other traders due to price changes. Both effects in these sections can be modeled using econometrics as f and g, but the nonlinear h in the final price change function h(f, g) is very difficult to obtain good upper and lower bound estimates.