There is an Android app called Simpleaf (probably also available for iOS). If setup properly, it can be opened at any time by dragging down on the notification bar and it overlays the SD chart. It can also be setup to open in translucent mode so that you can still see the chart. The app also has a button which, when tapped, cycles between translucent and opaque modes. You can make notes across multiple pages which are saved, even after closing the app, until you decide to delete them.

Mike
_________________________________________

The SkyDemon scratchpad isn't really designed for taking permanent notes. Have you considered using the quick notes feature built in to your phone or tablet? Certainly this is available on newer iPads, not sure about Android tablets.

I am FI and would like to take notes on the scratchpad during the flight.