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Greenwich Observatory magnetometer traces (horizontal force on top and declination on the bottom; the two traces are offset by 12 hours) during the time of the solar flare on 1 September 1859. The red arrows indicate the magnetic crochet or solar flare effect (SFE). Comparing the size of the SFE with modern large flares for which the SXR classification is known permits an estimate of the size of the 1859 flare. The writing at the bottom in the red box says "The above movement was nearly coincidental in time with Carrington's observation of a bright eruption on the Sun. Disc[overed] over a sunspot. (H.W.N., 2 Dec 1938)." The annotation "H.W.N." refers to Harold W. Newton, Maunder's successor as the sunspot expert at Greenwich.