This card is a color-change indicator and is reversible as required by Military Specification MIL-I-8835. As the humidity increases, the chemically impregnated spots change from a blue color (DRY), through a lavender, to a pink color (HUMID). As the humidity decreases, the spots change from a pink color (HUMID), through a lavender, back to a blue color (DRY). Each of these cards is accurate to ±5% relative humidity (RH) at 24°C. Other humidity combinations are available by special order.
The card ranges from 30% RH to 50% RH.