How are multiple trending charts and their control elements are referenced and distinguished on a single display?
Trending charts are distinguished by their "trend group id" which is part of their parameters list.
If you are using multiple trending charts on a single display and you want to control them separatly then they need distinction. So give each of your chart a different name.
If you want to add further controls to a trending chart like a start/stop button, CSV export button etc. then use the same group name id in those controls to assign them correctly.