An important point here is that "texture retention" is defined (per warranty) as "the ability of the carpet tufts to retain their visible shape, as measured by the degree of bursting, opening, or untwisting of the tufts at the surface of the carpet." It doesn't mean crushing or matting of the carpet pile, which is a typical result from use over time.

Texture retention is measured against standard rating scales per ISO Standard 9405-1990. This standard rates carpet texture from a 5 (no change from new) to a 1 (severe change).

Statewide Floor Covering Inspection Service uses a CRI Retention Rating Scale as an aid in assessing appearance change in carpet.  These scales are widely used in grading laboratory specimens, such as those tested in a Hexapod or Vettermann Drum tester, and also for grading floor traffic specimens tested according to ASTM D-6119.  This series of reference scales is a revision of those previously adopted.

Each set of scales consists of six sets of digitally imaged increments of change, representing a five-point scale with intermediate half steps.  It is important that the scale be used according to the recommended practice as outlined in CRI Test Method (TM) 101