This lecture covers the concept of GNSS corrections, focusing on the autonomous DGPS station, the Swipos correction service, and the Permanent Network Analysis Center. It explains the real-time calculation and broadcast of corrections, the integration of range corrections, and the analysis of GNSS coordinates. The lecture also delves into the monitoring of GPS satellites, the status of AGNES stations, and the validation of tropospheric parameters. Additionally, it discusses the principles of EGNOS, the architecture of the system, and the application of ionospheric corrections. The presentation concludes with a detailed analysis of the error estimation and correction modeling in GNSS systems.