NI 9401 counter setup

Hello All.

Sorry for the simple question but I am at a loss.

I am using NI 9401 on  cDaq 9189.

I am using the example code "Counter - Read Pulse Duty Cycle and Frequency (Continuous).vi" - attached to this message/

And I am having hard time to configure it.

What is the difference between: "Pulse Frequency Terminal" and "External Clock Source"?

For the counter I wish to use: "NI9401counter/ctr0"

for the setting that is shown in the screenshot:

I get the following error message:

hat your start trigger is configured correctly. It is also possible that you configured the task for external timing, and no clock was supplied. If this is the case, supply an external clock.

Property: RelativeTo
Corresponding Value: Current Read Position
Property: Offset
Corresponding Value: 0

Task Name: _unnamedTask<92>

Clearly I am missing a very basic thing here.

How do I make it work?

Thanks!

Gil,