This Maintenance kit is for a Agilent/Varian 525 Cold Cathode gauge. The 525 Cold Cathode ionization gauge tube, measures pressures down to 1 x 10^-7 torr with accuracy and reliability. When properly maintained, the 525 starts at very low pressures where ordinary cold cathode gauges are difficult to start. Excellent repeatability and improved stability are provided by the linear response below 1 x 10^-2 Torr (data sheet .pdf below on Agilent 525)