[en] We study the Quantum Measurement Process in a Stern–Gerlach setup with the spin of a silver atom as the quantum system and the position as the apparatus. The system and the apparatus are treated quantum-mechanically using unitary evolution. The new ingredient in our analysis is the idea that the probes determining the position of the silver atom are limited in resolution. We show using a Wigner matrix that due to the coarseness of the detection process, the pure density matrix appears to evolve to an impure one. We quantify the information gained about the spin in a coarse position measurement. - Highlights: • We focus on the role of limitation of resolution on quantum measurement in a Stern–Gerlach setting. • We show how coarse graining leads to a transition of a pure density matrix to an impure one. • We quantify the information gained in a coarse measurement in a Stern–Gerlach setting.