In some embodiments, the disclosure describes a catheter system for applying energy to a vessel, such as a vein. The system may include an elongate catheter shaft having a distal end and a proximal end opposite the distal end, and an energy application device coupled to the distal end of the elongate catheter shaft. The energy application device may be configured to apply energy to the vessel. The system may also include a gauge positioned relative to a working surface. The gauge may be configured to determine a distance that the elongate catheter shaft travels with respect to a treatment zone.
