You can route the signal to measure to the Source input of Counter 0, as shown in the following figure. Assume this signal to measure has frequency fx. NI-DAQmx automatically configures Counter 0 to generate a single pulse that is the width of N periods of the source input signal.
Next, route the Counter 0 Internal Output signal to the Gate input of Counter 1. You can route a signal of known frequency (fk) to the Counter 1 Source input. Configure Counter 1 to perform a single pulse-width measurement. Suppose the result is that the pulse width is J periods of the fk clock.
From Counter 0, the length of the pulse is N/fx. From Counter 1, the length of the same pulse is J/fk. Therefore, the frequency of fx is given by fx = fk * (N/J).