You should get a laser with a 360 horizontal beam make a pocket in the floor set 1/4 low in floor ...and you will see the beam projected on the floor and see all the high and low spots easily

Just flood the floor a bit and look for dry spots. You can then grind the high spots. No laser needed.

Stop spoiling the trade secrets Sir but this methoed is the best way to level floors from a 10+ year tile installer.

Best video on this task I have found thus far... well.. didn't find it per say, google recommendation based on numerous searches! But great, thank you!

Much easier to leave the level in one place and use a stick or a metal ruler and move that around the room

Semantics matter when doing flooring and many people are confused when the term "levelling" is used because that's really NOT what's important, FLATNESS is important. You can have a floor that slopes (not level) say 1, or even 1 1/2 inches from one side of the room to the other over say 16 ft. but that matters not because as long as the span is FLAT then the "out of level condition" won't be seen by eye. Bedrooms and even living rooms and family room oftentimes have this condition. Stop referring to flooring preparation as "levelling". Most concrete slabs are not "level", but they are FLAT.

Hi Bill, where did you buy 8-Feet Reinforced Aluminum H-Screed with Plastic Cap?

Was the vertical laser line to ensure you were holding the stick exactly vertical?

I just use a 12 or 16 laser level, shows you all the spots above 1/4 inch from the lowest spot on the floor. For a sloped floor, you can just use a small lift for the laser level and grind down high spots that don't follow the slope.

What brand/model of laser level are you using? How are you liking it?