The principles for position determination are trilateration, triangulation and fingerprinting. These non-traditional PAR systems use transponder multilateration, triangulation and/or trilateration. Geolocation on web-based social network services can be IP-based or use hotspot trilateration. The accuracy is better than estimations with trilateration based on received signal strength indication (RSSI). Aircraft DME/DME navigation and the trilateration method of surveying are examples of its application. A practical application involving a fixed location is the trilateration method of surveying. Both are often done in surveying when the trilateration method is employed. RF trilateration uses estimated ranges from multiple receivers to estimate the location of a tag. In surveying, "trilateration" is a specific technique. Errors in trilateration surveys are discussed in several documents. Multiple measurements can be combined with trilateration and multilateration to find a location. Most often, this is done through trilateration between radio towers. The principle of location is based on trilateration.