GPS Calculations involve two main processes: ETAS (Estimated Time of Arrival) and RTES (Real-Time Estimation System). ETAS is a method of calculating the estimated time of arrival for a vehicle or person based on their current location and speed. RTES is a system that uses GPS data to calculate the real-time position of a vehicle or person in order to provide more accurate estimates of their arrival time. Both ETAS and RTES are used in navigation systems, such as those found in cars, to help drivers reach their destination faster and more safely.