Recently Windows 10 went thru an interesting update / upgrade.
One new feature is the Windows Whiteboard. It replaces the old Sketchpad. I just started to work with it to plot and detail out charts.
So far it work very nice, it is better then pen and paper since you have clean Undo / Redo and you have instant pen changes. Another nice feature is that that the whiteboard is scroll-able and has zoom that is active with finger gesture. And you can save. The whiteboards are saved into a gallery so they are virtually available. Haven't work thru all the features / details yet.
If you work out charts with pen and paper this is a nice alternative and worth a look.