When you import data into the GUI, you must specify the data sampling interval.
The sampling interval is the time between successive data samples in your experiment and must be the numerical time interval at which your data is sampled in any units. For example, enter 0.5 if your data was sampled every 0.5 s, and enter 1 if your data was sampled every 1 s.
You can also use the sampling interval as a flag to specify continuous-time data. When importing continuous-time frequency domain or frequency-response data, set the Sampling interval to 0.
The sampling interval is used during model estimation. For time-domain data, the sampling interval is used together with the start time to calculate the sampling time instants. When you transform time-domain signals to frequency-domain signals (see the fft reference page), the Fourier transforms are computed as discrete Fourier transforms (DFTs) for this sampling interval. In addition, the sampling instants are used to set the horizontal axis on time plots.