For light resistance, loop a rubber band around the top bar of the sliding finger grip. Attach additional rubber bands to increase resistance. Five rubber bands are included, each providing approximately 4 lbs. (1.8kg) of force.
For even greater adjustability, try the Deluxe Hand Exerciser which includes two metal thumb screws to change the length of pull to best fit hand size or desired range of motion as well as foam hand grip for increased comfort.