It illustrates the results from some certified standard materials I analysed on the portable XRF machine yesterday afternoon. Certified standards are materials whose exact composition has been tested and agreed on by multiple laboratories, often the best international ones. We use them to check the accuracy of our instruments.
The x-axis shows the amount of zinc in a standard material that the portable XRF observed. The y-axis shows the amount of zinc that the material has been certified to contain. If you want to compare them directly you can just look at the raw numbers – in an ideal world the XRF result is extremely close to the quoted quantity.In the real world there can be some difference between the two.
The purpose of this graph is to see how the calibration and the instrument is behaving. The straight line fit is really good, indicating that whilst there may be some small difference between the analysis and the quoted quantity of zinc, that difference is minor and essentially the same every time, which means it can be very easily adjusted for. You don’t often see such a great fit as is demonstrated here. I wish all instruments were this solid!