Hi John, a servo motor have a maximum rotation angle from 180 degree. With a cogwheel you can use 360 degrees. You can use a servo for FTIT, Hyd. Pressure and other from this gauges. A stepper motor can rotate without limited, its a motor ;-) that rotates in many small steps.A stepper motor you can use for altimeter air speed indicator and other. Best wishes Martin "Pegasus"