put a link to navigate back to the stock from the chart page
There's no way to navigate back to a stock page from the large-chart page. The watchlist is on the right, but those links open only large-chart pages.
Bobby Miles commented
in full-screen the top-left back link is same as browser back function. IMO it shouldn't. I would change the top-left back link to link the user back to the current stock/security summary page.