how to write equation with voltage from channel 1 as input in math function of adalm 2000 (scopy)?

Sir 

 i want to plot current across a  diode  and resistor  .but i am confused to plot vi chara by math function.what is" to and t1"" in math function used for.is their any other way to plot current directly.what is meant by usage of shunt resistor to plot current.