In a small area without critical accuracy requirements, the old school approach of a stretched string with a chalk line and a bubble level can provide adequate measurements. For larger, more critical situations, laser technology provides a substantial improvement. A laser, such as the DeWalt DW074KD, a rotary laser level accurate to 1/4 inches at 100 feet, can be used for both interior and exterior measurements. With its companion detector, the beam can be recognized up to a 1200-foot diameter outdoors. Rotating at speeds of 0, 60 & 600 rpm, the laser has a self-leveling range of ±5 degrees.
More advanced laser levels use a green light instead of the red laser light (Class IIIa (<5mW) at 635 nm) and have an accuracy of ±1/16 in. at 100 feet and a range of 2,000 feet. The green light can be four times brighter than red laser beams but that comes with the price of greater power consumption for the battery-powered devices. The red lasers are generally more accurate and more reliable over a range of temperatures.
The laser line detector directs the user to position the laser higher or lower on an aluminum grade rod to ensure a level reading and provides an audible sound that increases in frequency near the level point. Some detectors have a leveling vial for manual leveling in vertical mode. In some laser levels, other capabilities include a dual-axis slope mode for added functionality, a scan mode of 15/45/90 degrees and an IP67 rated with a 2-meter drop for durability.