\section{Requirements}\subsection{Scientific Requirements}\subsubsection{Support \htmlref{no-leap}{glos:noleap} and Gregorian calendars}\subsubsection{Provide the following calculations:} \begin{itemize}\item Given a date, compute a new date that is either earlier or later by a specified time interval.\item Given two values of date compute the time interval between them.\item Verify whether or not one date is later than another.\item Provide \htmlref{calendar day}{glos:calendarday} given date.\end{itemize}\subsubsection{Handle time intervals to a precision of 1 second}\subsubsection{Handle time intervals with a range of 20,000 years}   \subsubsection{Date to string conversion}