Change rate of the inter-marker distance over time. The inter-marker distance increases, calculated by integrating the monthly distance changes over time, as a percentage of the total annual increase, for (a) the 3D and (b) 2D methods. The mean distance increase of all the marker pairs is shown in blue. The distance increase curves of the fastest increase marker pair (LC-CP) and the slowest marker pair (GO-PMF) are also shown. Note that the distance increase reached 50% of the total annual distance increases during the fourth and fifth months, and reached 80% during the seventh and eighth month.