<p>A method of varying the relationship between a scalar input parameter and a scalar output parameter, by: displaying a relationship between an input parameter and an output parameter as a curve on a computer screen; selecting at least one control point on the curve; and moving at least one handle associated to the at least one control point to vary the shape of the curve as the curve passes through the at least one control point, thereby varying the relationship between the input parameter and the output parameter.</p>
