The CS650-L has rods that are 30 cm long, and the CS655-L has rods that are 12 cm long. The difference in rod length causes some changes in specifications. For example, the CS650-L is slightly more accurate in its permittivity and water content readings, but the CS655-L works over a larger range of electrical conductivity. In addition, the CS650-L handles a larger measurement volume and provides good accuracy in low EC (electrical conductivity) sand and sandy loam. The CS655-L is typically more accurate in soil, works well over a wide range of soil textures and EC, and is easier to install because of its shorter rods.