Ever thought how luminosity is measured at CMS? This done using so-called luminometers which are detectors counting a certain process with known cross-section. These cross-sections are measured once a year during a special LHC setup that allows to measure cross-sections without knowing the luminosity in advance. The main feature of this set-up is that the beams are moved away from their usual head-on collision course during so-called scans. CMS performs several types of scans, which collectively form the Van Der Meer program, honouring the Dutch accelerator physicist who invented the essence of the procedure. It has been successfully applied during run 2, and will see its first run 3 edition from November 10th to 12th 2022. The luminosity team within the Ghent CMS group headed by Postdoc Joscha Knolle proudly participates in this effort. They communicate the program to LHC and keep an eye on the CMS performance by day and night to ensure the best data-taking possible.
