I'd like make more clear the question that I've aroused in topic 'shifting region'. But previously I say thanks for help. I want to keep the trend of the variable in rectangle area - for example last 700 values (each value take 1 pixel on axis X). With each new value of the variable I shall do the next: - calculate the coordinate on axis Y (according to the scale of the variable) - shift the trend to left (1 pixel) - append the new point to the trend on the right - and so on I have no a good idea (for the time being) of how to make a shifting in the best way. There was no problem like this in the MS-DOS mode.