These sterilization indicators are for use in steam autoclave cycles at 250 °F (121° C) and 273° F (134° C); they're an economical alternative to OK® strips but use the same reactive ink as an OK strip.
The correct endpoint is indicated when the entire length of the strip changes uniformly black.
Nonuniformity of color is easily observed.
There are 250 sterilization chemical indicator strips in a box.