According to this system, devised by Scaliger in 1583, each day has a sequential number following the natural number order, making it much simpler to calculate the length of time between two given dates as it only involves simple subtraction. By the same token, fractions of a day are shown as tenths and hundredths of a day.The Julian Day Number system starts on 1 January of the year 4713 BC:-1 January 1967 is J.D. 2,439,492;- 1 January 1968 is J.D. 2,439,857;- 1 January 1969 is J.D. 2,440,223.In most cases, the last four or five figures need only be remembered.