Evaluate optical density to get concentrations of your ELISA

Today I was doing a quick ELISA and realized that the reader was old and produced the results in PDF only. This poses multiple problems as they need to be manually rewritten to a file and post-processed later. Additionally the optical density measurments in my software are automatically calculated into concentration based on some shady functions which I never understood. I decided to change this and learn this and that about analysing ELISA results.