Why will the counter not make low frequency measurements?

Verify the System Timeout setting by pressing Utility - Instr Setup - Time Out Settings. Turn the time out off or set it to a value much greater than the period of the signal (e.g. 10s). The system time out prevents the counter from hanging should the measurement fail to complete. A value of 9.91E+37 is returned for the incomplete measurement and the next measurement begins. The system time out is turned off when the counter is shipped from the factory.