Advanced Date Time Calculator

A full-featured date time calculator that contains 5 main functions: calculates the result time by adding/subtracting some years, months, weeks, days, hours, minutes and/or seconds; calculates the differences (years, months, weeks, days, hours, etc.) between two times; counts the days of week, weekdays, weekends between two dates; Gets the conversion between various date time elements; Calculates UNIX date based on a large days/seconds number.