As a scientist, I often read others’ scientific writing and work. Typically such written work includes plots and graphs — much more efficient and insightful ways of showing data than extensive tables. However, sometimes it’s important to extract more exact values from such plots. Traditionally this was done with a digitizer, a fancy mouse that worked on a special pad. You’d place a printed figure on the pad, and use the crosshairs on the mouse to pick out points. Then, using some scaling calibration, you’d derive values from points on the graph.
GraphClick does the same thing, but with digital figures. Typically, I use it with figures snapped directly from PDFs of papers, though it would work just as well with figures scanned from hard copies. Rather than explain more about how it works, I’ll direct you to the screencasted tour.
GraphiClick is a commercial, closed-source application, but it is available for free use with a limited feature set. I never found in using it that I needed any of the more advanced features. If you ever need to pull data from figures, and you’re a mac user, I highly recommend you try it out. I used it extensively for my soon-to-be-published paper, and I couldn’t have asked for anything better.