Laser light can damage your eyesight. Don’t look directly into the laser light.
The idea behind the laser cross-hatch is simple. You’d like the tweeter to be aimed pretty much directly at your ear – small changes of the speaker’s distance, height, setback, and toe-in angle are all pretty critical to make even between left and right ears. This laser device makes it easy to get everything but the distance from the speaker to your ear correct.
I have found that there are other measuring devices to do this, but the most accurate—as well as the simplest—is a good old tape measure.
Once you’ve managed to angle, level, and point the tweeter equally at both ears while in the listening position, the next step is to decide if that’s actually right for your system, room, and musical tastes. By this statement, I mean that an on-axis response (aiming the tweeter directly at the ear) isn’t always what you want.
If the sound is too bright and you’re confident it isn’t the electronics that are responsible (as it often is), the next best thing is to take the tweeter off axis (not pointing directly at your ear). This is typically achieved by pointing the tweeter higher. My recommendation is placing something like a CD under the front of the speaker cabinet, tilting the box back—which has the effect of pointing the tweeter slightly higher. Check your work with the laser. The more off-axis, the less bright and intense the speaker’s top end.
Equal is critical. Whatever on or off axis you wind up with, make certain the amount is equal between right and left ear.
One last note. If you are performing the final tweaks by yourself, or if you’re concerned about the laser light, make a cardboard cutout that replicates your seated height. If you’re conscientious about measurements, both of your seated height as well as the position of your ears, then the cardboard cutout really makes things simple.