All chart windows in Optuma include an icon in the top-right corner of the page used for pinning charts:
To pin a chart in place, left click the pin icon once. The icon will update to show the chart is now pinned:
When a chart has been pinned to the page, it will always display over the top of any other (unpinned) chart. Adjusting the tiling orientation will also have no effect on the size or position of a pinned chart, so it is a great way to protect your preferred page layout when wanting to make modifications (such as adding an additional chart).
The above example shows a small chart of the XAO which has been pinned above a chart of CBA. You can adjust the view on the chart, and even apply tools without the pinned chart being hidden from view.