A cellular-type PD unit is proposed and a plurality of the cellular-type PD units is used in pairs in a multi-axis magnetic lens for focusing a plurality of charged beams. One embodiment of such a method comprises positioning a cured fiber-cement workpiece over an anvil plate having at least one slot and driving a cutting blade along a straight, vertical path to pass a cutting edge of the cutting blade through the workpiece. Preferably, one of the bodies is made from soap and may be used as a tub toy for, for example, a child. More particularly, the model is constructed from the Jacobian matrix characterizing a change in measured color output for a change in input color values of the pixel.