Methods of designing an earth-boring tool are described, including calculating one or more performance parameters based on drilling conditions, a plurality of wear state values, and a set of values of other design variables. In one embodiment of the invention, the control system can include a first control link that transmits control inputs between at least one control input device and at least one control output device and a second control link, at least one portion of which is changeable from a disengaged state to an engaged state, the at least one portion being inactive when in the disengaged state. In one embodiment, the display member is fabric. This use of a mask has some disadvantages, some of which can be overcome by utilizing an array of suitably shaped individual electrodes instead of a continuous one; however, this itself has drawbacks, since the lead to each electrode acts as an electrode in its own right, activating the phosphor to show faint but distracting additional illumination.