Redraw four curves (axis) from scan to vector

I have a scan of the old document with a few curves (or rather axis). I need them in vector format (i.e. PDF, AI, SVG, etc.).
It is not about automatic (computer) tracing, but the have to be manually redrawn from the scratch as they are not clear/visible enough.
The vector version must be good, much better than original.

Time is not important - a few dans would be OK.