Official websites use .gov
A
.gov website belongs to an official
government organization in the United States.
Secure .gov websites use HTTPS
A lock (
) or https:// means you've safely
connected to the .gov website. Share sensitive
information only on official, secure websites.
Relative darkness = gray value of measured area/255 × 100%. The dotted lines indicate background darkness value of the white body, above which the tanning is visible.
