Modulation of the ion current in Bayard-Alpert gauges allows operation at pressures below the normal x-ray limit and the measurement of pressures of electronically desorbable gases (e.g., O2, CO, and Cl2). Modulation by the method originally proposed (mode I) has two undesirable features: (a) modulation may cause pressure bursts, and (b) some modulation of the x-ray photocurrent occurs. Various alternate modulation methods are examined to determine which method minimizes the undesirable effects. A modulator external to the grid is only effective with electron currents less than 5 mA and with an open end grid. Two methods using a modulator internal to the grid are shown to be satisfactory; in the first (mode II), proposed by Lange and Singleton, the ends of the grid are left open and the modulator is switched from grid potential (Vg) to about (Vg − 20) V. In the second (mode III) the ends of the grid are cloud and the modulator is switched from (Vg − 20) to (Vg − 60) V.