How to capture a device LCD to number


I want to find a solution to convert any handheld instrument digital readout into a data stream that it can plot as a chart based on a preset time interval like this:

LCD to number chart

Using a webcam to capture and dump the data to a spreadsheet to plot the chart. I did look into source code like ssocr, capture2txt etc, but none of them can do a complete solution. Any suggestions welcome. Thanks.