The backbone of the Amsterdam Ordnance Datum (NAP) is a network of about 400 primary subsurface markers. Relative movements between the primary subsurface markers are measured with spirit levelling once in 10–20 years. We investigated absolute movements in this primary network through a time series analysis of more than 20 years of gravity measurements at 4 stations in the Netherlands. The result is important for the interpretation of the water level measurements along the Dutch coast.