What is the crowd's opinion of Engauge Digitizer?

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I do not have any but you can find pictures of curves on the internet or papers. You can then convert them back to XY data using a plot digitizer. Engauge is open source and has worked well for me in the past. Hope this helps

Whenever I need to digitize a plot, I use Engauge: http://markummitchell.github.io/engauge-digitizer/

It's a free tool that lets you load in an image and it will either try to convert lines and points to a data table or you can click on points individually and it will generate the table. Very handy. Then you can get trendlines in excel or do your own regression in MATLAB or whatever else.

I can’t guarantee this will work but try:

http://markummitchell.github.io/engauge-digitizer/

To digitise the charts then you could try using excel or more specialised software to fit a function to the individual curves.