This product effectively demonstrates the laws of reflection and refraction. The 16cm diameter acrylic water tank has a 360 degree scale and a moveable arm carrying a laser activated by a push-button. Thumb screws on the side of the laser harness can be adjusted to finely position the laser beam. Requires two AAA batteries (not included). Includes activity guide. Please Note: This product emits laser light. Max. ouput power<1mW. Wavelength 630-680nm. Class II laser product.