IP rating (short for Ingress Protection) is a standard that's used internationally to indicate the effectiveness of the ceiling against water, moisture, dust, and dirt. 2 digits are set to give you an idea about the dust and water resistance. It would go from 0 to 6 for dust and from 0 to 8 for water. Here is how it goes: 0: not protected 3: protected from particles > 2.5mm 4: 1mm particle protection 5: dust protected with minimal dust intrusion 6: dust-tight A significant number of laser levels are rated from 4 to 6 for dust resistance. A laser that has an X instead of a number is not rated for dust. The second digit indicates the water resistance. Here's how it goes: 0: no protection 2: protection from dripping water 4: protection from water sprayed in all directions 5: higher water pressure 6: streaming water 7: short period of immersion 8: full water submersion protection. It's essential to keep in mind that even with the highest rating of water resistance, it is advised that you keep the laser level as dry as possible. Constant exposure to water will still cause damage.