The CS506 is a fuel moisture sensor that measures the moisture content of the 26601 10-hour fuel moisture stick. The 26601 emulates the moisture content of similarly sized twigs on the forest floor. The CS506/26601 combination is used to assess forest fire fuel and is often incorporated in our prewired or custom fire-weather stations. Note: The image shows a CS506 fuel moisture sensor attached to a 26601 fuel moisture stick. The 26601 is purchased separately.