clause 20 wherein the calculation of the non linear function is performed by a program running in the back ground mode of the computer 22 method according to clause 21 wherein the result of the non linear transformation is converted into the output displacement signal by a motor driver circuit of the computer 23 method according to clause 22 wherein the motor drive signal is a step like analog direct current 24 method according to clause 22 wherein the motor drive signal is a pulse signal 25 method according to clause 24 wherein the motor for displacing the platform is a stepper motor 26 method according to clause 23 wherein the motor for displacing is the platform is a servo motor 27 method according to clause 1 wherein each motor displaces the platform by a spindle arrangement having an end switch to stop the motor at an extreme displacement position of the platform 28 method according to clause 27 wherein adjacent wells of the spindle have a distance of about 4 mm and the motors allows for microstepping of about 40 000 steps per revolution 29 method according to clause 20 wherein the platform is provided with position read out facilities connected to the computer in particular the position read out of a servo drive mechanism is coupled to the computer 30 method according to clause 29 wherein a button allows for memorizing in the computer the position signals of the position read out facilities 31 method according to clause 30 wherein.