Hi ND,
The Time/Div knob on the soft front panel is used to determine the sample rate of the acquisition. The Time/Div knob multiplied by 10 (Specifically on the Soft Front Panel because the graph has 10 sections) to give you the total acquisition time. The soft front panel takes the total number of samples (Edit » Device Configuration and under the Horizontal Tab there is the record length) divided by the total acquisition time to programmatically determine and set the sample rate. If you are using LabVIEW, you will need to setup your graph to a specific number of sections and total size to accomplish this task. You will also need to programmatically set the sample rate for each acquisition based on the record length and Time/Div value. If you are using LabWindows CVI, take a look
here at another thread that discusses a way to implement the knob.
I hope this helps,
Paul C.