If you look at the "Beginners Guide" that comes packaged with PLX-DAQ-v2 there is a command called CELL,GET, this is a command sent from the arduino, the Excel app responds with the value of the specified row + column. Although it does not show in the example you might realize that if the row value is replaced by a variable you would be able to retrieve different values from the desired column at any particular time period you set in your arduino code.