Summary Experiments Have Been Made to examine the influence of the geometry of the electrodes on the performance of coldcathode, or ‘Penning’, vacuum gauges. The arrangements reported include (a) disc cathodes and ring anodes, (b) ring cathodes and ring anodes, (c) disc cathodes and cylindrical anodes, (d) disc cathodes and wire anodes. In addition gauges with multiple ring anodes and multiple cathodes have been examined. The bearing of the magnetic field on the performance of these instruments has been assessed. The broad conditions of stability are clear and it is shown that the pressure at which changes of mode take place can be controlled and, with some arrangements, eliminated at the expense of a small loss of sensitivity.