Table 2. National Bureau Standards (NBS) interpretation of color changes.

NBS unit	Color change	Clinical interpretation
0.0–0.5	Trace	Extremely slight change
0.5–1.5	Slight	Slight change
1.5–3.0	Noticeable	Perceivable
3.0–6.0	Appreciable	Marked change
6.0–12.0	Much	Extremely marked change
>12.0	Very much	Change to another color