This is ideal for taping to a wall over distances greater than arms length. It allows you to see when a laser line is level, either horizontal or vertical. 

Steps in using this:

1. You tape this to the wall at the right height
2. Project your laser line further along the wall (say, 10ft away)
3. Mark the wall on the projected laser line out to arms length (say, 4ft away)
4. Move the laser level to the line you just marked (4ft mark)
5. Repeat step 3 until you have a line that runs the entire length of the distance you need.