In ordering the compulsory termination of a nonconforming structure or nonconforming use, the Town Board will establish a definite and reasonable amortization period during which the nonconforming use may continue while the investment value decrement resulting from the termination is amortized. Determination of the amount to be amortized shall be based on the value and condition of the land and improvements for the nonconforming use less their value and condition for a conforming use, and such other reasonable cost as the termination may cause. The rate of amortization shall be in accordance with reasonable economic practice.