Four panels comparing the variometer declination measurements in the Netherlands to the magnetograms from Greenwich and Kew evaluated at the corresponding variometer timestamps. From left-to-right then top-to-bottom the comparisons are: Greenwich (x-axis) to Utrecht (y-axis), Greenwich (x-axis) to Den Helder (y-axis), Kew (x-axis) to Utrecht (y-axis) and Kew (x-axis) to Den Helder (y-axis). Perfect correlation guidelines are displayed in black. The stars indicate measurements done during the two magnetic storms, i.e. between 28–30 August and 2–4 September. The Pearson correlation coefficients (r) are calculated twice: excluding (dots) and including (dots and stars) the storm measurements. Their values are listed in the sub-figures (including storm measurements denoted between brackets).