Halcro,
Just measure from the spindle to where the mark hits the wall and the calculator should get you very close. I don't believe that the beam needs to be exactly perpendicular to the wall for this to work well enough. However, the accuracy of the data input into the calculator is important. Try to measure as accurately as possible as that's going to be the source of the most error.
Just measure from the spindle to where the mark hits the wall and the calculator should get you very close. I don't believe that the beam needs to be exactly perpendicular to the wall for this to work well enough. However, the accuracy of the data input into the calculator is important. Try to measure as accurately as possible as that's going to be the source of the most error.