1. A method of estimating a maintenance date for a tool based upon a parameter of the tool, comprising: obtaining a difference between a detected value of the parameter and a maintenance value of the parameter; determining whether the difference is less than or equal to a predefined value; performing a maintenance procedure if the difference is less than or equal to the predefined value; and estimating a maintenance date according to the difference and a variation value if the difference is greater than the predefined value, the variation value representing a change in the parameter per time unit.