Several European kingdoms lost 10 days, jumping from 4 October to 15 October, when moving from the Julian to the Gregorian calendar in 1582. Over the course of 16 centuries the Julian calendar had fallen out of sync with the Solar calendar by 10 days as a result of having 365.25 days as opposed to the 365.24219 days in the Solar year. (http://bit.ly/32zSHVO)