Older drift charts

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GRS and Hollow, 1830-92
Red dots, centre; blue "<", p. end; green ">", f. end; black dotted line, zero meridian of System 2

GRS, 1964-2007
in System 2, 60-day running means

Long-lived STC White Ovals, 1970-2006
Blue, BC/BE/BA; brown, DE; green, FA; red, GRS

NEqC, 1977-79
Black dots, dark features; red dots, bright features

Beer and Mädler's spots, 1834/35

NTrC, 1884-1900
Black dots, dark features; red dots, bright features; green line, zero meridian of System 2