Humidity indicator cards are designed for commercial use. Standard cards are inexpensive, yet small (1-1/2 x 4-1/2 in.) and easy to read. They provide an accurate assessment of the humidity level in a given area. You may choose to use the strip of tape provided on the rear of each card. Humidity scale changes for deep blue (dry), through lavender, to pink (humid) and back as the humidity fluctuates. Sold in packages of five.