What do laser classes 1, 2, 1M, 2M, 3R, 3B and 4 mean?

Class 1: completely safe even on direct viewing. Class 1M: eye-safe except when viewed through magnifiers or binoculars. Class 2: visible, up to 1 mW, protection via blink reflex (max. 0.25 s exposure). Class 2M: like Class 2, but not to be viewed through magnifiers or binoculars. Class 3R: up to 5 mW in the visible range, increased risk on direct viewing, safety goggles recommended. Class 3B: up to 500 mW, direct exposure dangerous, safety goggles mandatory, diffuse reflections usually harmless. Class 4: > 500 mW, dangerous even via diffuse reflection, highest safety measures, fire hazard. From Class 3R a laser safety officer is required.