How does Normalisation work?

There are three normalisation methods. Total Ion Current works by adding up all the values in each spectra, averaging these totals and then multiplying each spectrums values so their total now equals the average.

The other two methods use a single peak to normalise by, one which has been spiked into the samples. They assume this single peaks volume or peak height should not change between spectra. Therefore each spectrums values are multiplied so the volume/peak height of the spiked peak now equals the average of the peak across all spectra.