Hi I have had a look at your attachment.
A couple of things, firstly the 3205 measures a maximum of +/-20V however I assume you have scaled down the voltage.
Putting measurements at once every minute will (taking as many readings as possible) will give you an average for that minute. If however you chose "single" "readings per sample" it will take one measurement every minute.
It would be helpful if you could give me a better idea of your set up. I would also recommend downloading our latest software to see if this helps.