HP 809C Universal Probe Carriage is a precision-built mechanical assembly designed to operate with a number of interchangeable slotted lines. These include HP 810 Series Waveguide Slotted Sections and the HP Model 816A Coaxial Slotted Line. This carriage may also be used with the older Model 806B. The unit has a centimeter scale with a vernier reading to 0.1 millimeter. Provision is also made for mounting a dial gauge when more accurate readings are required. The probe carriage moves on two ground stainless steel rods and a ball bearing forms the third point of suspension.