The charts are actually added to your profile page or to your Baby Page, not to the tracker page itself. To add the charts, go to the page you want to add it to (profile or Baby) and then click the Page Settings button in the upper right. The button looks like it has gears on it. Then look for the Weight Percentiles Chart and the Height Percentiles Chart and add them.
Since you're new to MedHelp, you may not know what Baby Pages are, so I've included a link to more information about Baby Pages. If you would like to add a Baby Page, click the little "+" tab next to Profile and click Baby Page. If you decide to add a Baby Page, all the related Baby widgets will be automatically added for you, including the Weight & Height Percentiles, Immunizations, About Baby, and a ticker to countdown to the baby's birthday.
Please let us know if you have any further questions.