Instruments for counting local lightning flashes are reviewed and reasons are given for selecting one particular design for extensive tests. The importance of the aerial configuration is stressed. A 7 m vertical aerial has been adopted as a standard, and the instruments have normally been adjusted to trigger on a 3-volt signal from a built-in calibrator, corresponding to a field change of about 3 volts/m.With this arrangement, on a day on which thunder is heard, there is usually a maximum hourly count exceeding 30 and a total daily count exceeding 100.The effective range of a counter is defined in statistical terms and techniques for its measurement are discussed. Preliminary estimates of the effective range are derived from observations on a few local storms in England; with the standard instrument it is about 30km. More observations are required to confirm the results, particularly in countries with frequent thunderstorms. Equipment should be standardized so far as possible.