Hello Amir, Thank you for contacting National Instruments.
I am assuming that you are building X and Y arrays using shift registers within a loop and using these arrays as the inputs to the Express XY graph VI. If this is the case, during every iteration of the loop, the XY graph essentially redraws all data (new and pervious). As you accumulate more and more data, this process slows down considerably as the XY Graph has more to plot. You may want to consider using a chart. A chart does not re-plot all of the previous data in the way a graph does. A chart plots one point at a time as it arrives. I hope this helps! Let me know if you have further questions. Matthew C Applications Engineer National Instruments
