The Agilent 563 Bayard-Alpert hot-cathode ionization gauge tubes employ a heated filament for the source of electrons. The gauge tube offers superior performance over a pressure range of 2 x 10-10 to 1 x 10-3 torr. The inside of the glass body is platinum-coated, shielding the gauge elements from electrostatic charge at low pressures while draining off the static charge that can build up at high pressure. A reference gauge tube is also available, sealed off at ≤ 5 x 10-6 torr for use in testing a gauge controller.