My task is to estimate / compute accuracy of a gps receiver. My experiment would involve using three GPS receivers and post processing software. following is the nomenclature i would follow for explaining my question. Normal GPS receiver: This is the receiver in test, a simple 12 channel receiver with facility to log data for use later in post processing software Mobile DGPS receiver: This is the GPS receiver with data logging feature which would be carried along with normal GPS receiver in test in a vehicle. Base station DGPS receiver: This is a static GPS receiver placed at static location with most accurately known coordinates, whose data would be used for post-processing My doubt is about following aspects 1. I will move in a vehicle with separate normal GPS receiver and mobile DGPS receiver on board. Maximum radial distance would be 200km from Base station DGPS receiver. My doubt is that GPS receiver and DGPS receiver may look at completely different satellites compared to the satellites tracked by the receiver at the base station of the receiver. After coming back to the base station, i will download the GPS and DGPS data from respective receivers. i will use the data from mobile DGPS receiver along with data from DGPS base station receiver to calculate the accurate coordinates of the mobile DGPS receiver after post processing. Can i compare the data from normal GPS receiver and DGPS receiver for error calculation, assuming that the DGPS data is most accurate. My comparison would be at a particular instant of time DGPS gave XX coordinates, the coordinates given by normal GPS receiver is XX coordinates, the radial distance at any instant of time is the error the normal GPS receiver which is in test, is this the accurate means of error estimation or calculation ? 2. My second doubt is that i learnt that gps receiver calculates its time by acquiring signals from various satellites. I understood that if the satellites the two receivers acquire signals from are different, then the receiver time solution they arrive at would be different i.e. the receiver time the two GPS receivers calculate would be different. In such a case my doubt is that the coordinates of the two receivers at any instant of time cannot be compared for error calculation of the other receiver as explained in earlier question of mine. i mean to tell that the receiver times of an two receivers would ideally will never match theoretically, at least there would be at least few nano seconds difference, is it true? 3. Apart from the above reason for receiver times not matching, also if the method/algorithm for solving the GPS pseudo range equations is different than the solution they arrive at would be different, is it a true statement?