A Semi-Automatic Construction Laser is a laser model that self levels via a wire hung compensator.  These are gravity pendulum leveling mechanisms that must be rough leveled via 2 or 3 leveling knobs.  Once the instrument is in its self-leveling range, the pendulum compensator makes sure the beam is level.  An example of this type of construction laser is the ProShot L4.7.  Many of my contractors like this type of laser as with a pendulum leveling laser you have less moving parts.  Less moving parts means less down time and fewer repairs.

An auto construction laser is a laser model that automatically self levels with a touch of a button.  No leveling screws are required. Many of my contractors prefer this type of leveling as it is much easier to set-up.  I call it one button simplicity.  Also, if a contractor needs a Grade Laser, they only come in the auto leveling format.  Examples of this type of self leveling is the Pro Shot Alpha, Leica Rugby 600 series or the Leica Rugby 800 series lasers.