Nicolaus Keim died Aug. 25, 1802. His age at death is list as 82 yrs. 4 mo. and 23 days. His birth has always been listed as 02 April 1719, but when I used my birth calculator, Nicolaus's birthdate figured out to 02 April 1720. Is this because of the double dates thing? Can someone explain what the "double dates" refers to?