How to check the surface of the subfloor

Before flooring, we need to check the surface of the subfloor if it is suitable for flooring on directly.

Planeness. When a straightedge 1.5 m long is placed on the surface at any position, no part of the surface shall be more than 6 mm below the straightedge.

Smoothness. When a straightedge 150 mm long is placed on the surface at any position, no part of the surface shall be more than 1 mm below the straightedge.

It’s an easy way to do before starting flooring.