Standard rectangular cards are available as low as 5% and 8%. Humidity Indicator Plug cards are only as low as 10%. This is because establishing the color of the card in the plug is more difficult than reading a card that is in your hand. The lower 5% and 8% values are difficult to read due to the small amount of chemicals present, which results in a very low-density coloration. Think of a particular color that has had much more white added to it.