And the best, most accurate laser in the market for this application is Hamar Laser’s  L-740 Ultra-Precision Laser Alignment System, which features:

• A continuously rotating laser plane significantly that speeds up the measuring process, allowing leveling and flatness measurements to be done up to 70% faster than traditional methods.
• Flatness accuracy up to .000015 in/ft. (0.001 mm/m) provides the ultimate in accuracy for leveling machines and checking flatness.
• Leveling capability up to .00006 in/ft. (0.005 mm/m).
• Two methods to check flatness:
  1. Level Vials – Use our built-in 1 arc-second level vials to level the laser and check the surface for flatness relative to a level earth plane.
  2. Reference Points – Align the laser plane to 3 reference points on the surface and check the rest of the surface for deviation from the reference datum plane
• Wireless A-1519-2.4ZB Target Sensors with
  • .00002 in. (0.0005 mm) resolution
  • ±.55 in. (±14 mm) measuring range
  • wireless range up to 150 ft. (45 m)
• Data sent wirelessly to rugged R-1357-2.4ZB Android PDA or Windows PC.
  • Use multiple A-1519-2.4ZB targets simultaneously on large machines or surfaces to further speed up the alignment process.
  • Real-time alignment data speeds alignment by updating as the machine is adjusted to see when your machine comes back into alignment.
• Windows-based Plane5 Software analyzes data and can run on any Windows tablet or laptop.
• For lower accuracy applications, please see our L-730 Precision Leveling Laser  with a laser plane flatness of .00012 in/ft. (0.01 mm/m).