The multi-constellation GNSS RTK receiver can use 12 GPS, 8 SBAS, 6 BDS, and 1 QZSS signal. In situations where RTK fix is not possible, a Float RTK mode can be used for decimeter-level accuracy positioning. A moving-base mode is also supported for precise heading GPS compass application. The device measures 25 x 25 mm, weighs 3 grams, and draws only 250 mW. It supports both base station and rover modes. As a rover, it receives RTCM 3.0 or 3.1 data from a base station, or raw measurements from another S2525F8-RTK receiver serving as base station, and performs carrier phase RTK processing to achieve relative positioning with 1cm + 1ppm position accuracy within 10 km baseline, and decimeter-level accuracy for over 10 km baseline can be achieved using Float RTK mode. Two S2525F8-RTK receivers can be used to form GPS compass that provides 0.17-degree heading accuracy at 1 meter baseline.