Only reason I didn't give it a higher number was that I think the "nubs" on the underside designed to keep the mat in place on the carpet they could be a bit smaller - when rolling across the mat on the desk chair you can feel the "nubs" and over time this is where the mat fails cracks and needs to be replaced.
Mat was shipped in a box twice as big as necessary. Result the chair mat was all crumpled. Followed instructions to flatten. Still has creases/lumps in it