As for small molecule analytes, in-source fragmentation effects are of paramount importance for correct data interpretation. Think about problems arising with database searches or machine learning algorithms are trained on datasets recorded with different activation conditions. Although several authors proposed to use thermometer ions to monitor, standardize and control in-source fragmentation , they were probably right too soon, and their recommendations were not acted upon. The urgency is however now recognized, and in the wake of recent efforts to standardize MS/MS activation conditions , it is urgent to tackle the problem of internal energies and fragmentation at the interfaces of supposedly "soft" ionization sources.