Complete apparatus has a 15 cm adjustable scale, marked in mm, to help prevent parallax error Scale is mounted on sturdy 30 cm support rod Apparatus is situated on a sturdy wooden base Includes 9 slotted masses and hanger, each weighing 10g, for a total of 100g Ideal for demonstrating Hooke's Law which states the force needed to extend or compress a spring by some distance is proportional to that distance