The user interface provides three links to change the scale. Clicking on one of those link should change dateformat and groupby options. Here is the code:
Another problem is that when the new scale has only one element, it seems that extjs chart doesn't work anymore.
I try to explain better:
consider to have a daily chart showing the evolution from 1-03-2011 to 15-05-2011; in this case changing scale to month will show a line with 3 points:March 2011, April 2011 and May 2011.
But if the daily chart goes from 1-03 to 15-03, changin to month scale should produce only one point (March 2011). This doesn't work. And after clicking "month", no other chart on the page will work anymore.