The PLS 4 red beam laser level projects points up and down over a raised cantilever with a cross line laser on the opposite end.

Check Level Lines

Choose two interior walls approximately 15'-0" apart (see Fig. 1). You can use 2 x 4s for targets.

Turn on the PLS4 to setting #1 (level). With the PLS4 six inches away from and facing target #1, carefully mark the center of the line. Label this mark A1. Swivel the laser 180º and mark the center of the line on target #2. Label this mark B1.

Move the PLS4 six inches away from and facing target #2. Carefully mark the center of the line. Label this mark B2. Swivel the laser 180° and mark the center of the line on target #1. Label this mark A2.

You now have two centers of elevation at each target. Carefully measure the distance between centers of each set of marks. If there is a difference, subtract one measurement from the other. This calibration method magnifies any error by a factor of two. Therefore divide any difference by two to find the true error. Your PLS4 should have an error of no greater than 1/8 in. within 30ft. Check Plumb
 

Lines Choose a door jamb with 8'-0" clear on each side of the door. Turn on your PLS4 laser to setting #2 (plumb). With your laser at point A, make two marks on the floor: the first at 8'-0" from point A centered on door header above (mark this point B), the second 16'-0" from point A (mark this point C). Without moving the laser, make a third mark on the door header (mark this point D). Move the laser to point C, exactly align the beam with point B, and notice where the beam falls at point D. If it is within a "light" 1/16" of point D, the laser is in calibration.

If level & plumb are within specification, square will be in specification.​

Points Check of Plumb Accuracy. This requires significant vertical height (minimum 10'-0") and the ability to mark at that height. Place the unit with the down beam exactly centered on both axes over a cross mark. At the surface above, mark both axes of up beam. Rotate the laser 180° and place the down beam exactly centered on the original mark. The up beam should be exactly over the original mark. If there is a difference between marks the error of the plumb beam is one half that difference.