This product effectively demonstrates the laws of reflection and refraction. The 16 cm diameter acrylic water tank has a 360 Degree scale and a moveable arm carrying a laser activated by a momentary switch. The sharp beam of light produced by the laser can be adjusted to pass the center of the scale. Batteries and activity guide are included. Please Note: This product emits laser light. Max. output power1mW. Wavelength 630-680 nm. Class II laser product.