GPS positions only approximate. Comparison between GPS and DGPS determined velocities of Nordenskioldbreen. Vav is calculated using Eq. (1), with np = nv = 240. Vbe is based on the distance between the 240 h averaged beginning and end points of a GPS and Vdgps is based on the yearly DGPS measurements. GPS values are calculated over the same period as spanned by the individual DGPS observations, which is about one year. Uncertainties in the GPS determined velocities are based on the standard deviations in the 240 h average locations.