I created a new VB project, added a graph (Measurement Studio version 6.0) to the form, added a button, double-clicked on the button, and added the code that you posted. The problem did not reproduce for me - I saw a continuous line.
What version of Measurement Studio are you using? Also, you could post a project that reproduces this project? Maybe there are some other properties that are set that are influencing this behavior.
- Elton