Dear All, I'm a very new beginner in VB.NET. I should make a program using VB.NET as part of my dissertation. This program is a wait system simulation, there's a window (form) with a textbox (for the parameter Cb), 2 buttons (start and delete) and a picturebox (the place where curves will be shown). The X-Axis is for the "Rho" (from 0 to 1, and constant) and Y-Axis for "Teta" (not constant). If i give the value of the parameter Cb in the textbox and click the button "start", i can see the curve in picturebox automatically and the name of the curve (example: Cb = 0.5) will be shown too. If i give a new value of the parameter Cb, i will have a second curve in the picturebox but i can do this process just 5 times (5 curves with different colors in my picturebox) after that i have to click the button "delete" to clear all the curves and beginn a new process. The Formula is: Teta (Rho,Cb) = (Rho / (1-Rho)) * ((1 + Cb²) / 2) By the way, i'm a student from germany and sorry for my bad english :), many thanks for your helps ZA