What's the difference between red beam and green beam lasers?
Green beam is 4-5 times brighter to the human eye and has a longer range.
They can be used for outdoor work and an ideal option for indoor applications where light is low.
Considering green beams have an extra component, they take more time to produce and they consume more battery power. This makes green beam levels more expensive.

Red beam levels operate with a receiver which detects the laser. 
They are recommended for outdoor work, bright conditions and for distances beyond 10m.
Red beam has a longer battery life and doesn't require as much power.

What are IP Ratings and how to read them?
IP rating codes, also known as Ingress Protection or International Protection ratings are used to classify the different levels of sealing effectiveness provided by an electrical enclosure against foreign bodies such as tools, hands, dirt and moisture.
IP ratings have two numbers.
The first relates to solids such as dust and has a maximum rating of 6.
The second relates to liquids and goes as high as 8.
IP55 and IP65: Protected from most dust and low pressure water.
IP67: Dust-proof and resistance to water up to a depth. 

When does my rotary laser need calibrating?
Calibration re-test and certification is recommended every 6 months or at least once a year by an authorised service centre.
If your rotary laser has received a knock, the accuracy can be self checked to determine if a re-calibration is required. Self Check Your Rotary Laser Accuracy