Calc Object Function datediff() - calculate the difference between two dates
 
   Format:
     datediff(<diffType>,<datetime1>,<datetime2>)
       <diffType> is a string literal or string variable
         'YEAR'      - Calculate the difference in years
         'MONTH'     - Calculate the difference in months
         'DAY'       - Calculate the difference in days
         'WEEK'      - Calculate the difference in weeks
         'QUARTER'   - Calculate the difference in quarters
         'HOUR'      - Calculate the difference in hours
         'MINUTE'    - Calculate the difference in minutes
         'SECOND'    - Calculate the difference in seconds
 
       <datetime1> and <datetime2>
         In a Calc Object context, these values can be:
           . jdate() of a DATE field;
           . A DATETIME field;
           . A numeric variable derived from the jdate() of a DATE field;
           . A numeric variable derived from a DATETIME field;
         In a Calc Object context or a TQL context, these values can be:
           . jdate() of a DATE string literal or variable;
           . jdate64() of a DATETIME string literal or variable;;
           . A numeric variable;
           . Literal 0, which gives the current date and time;
 
   Result:
     The result of this function is the integral difference of the specified
     <diffType> of <dateTime2> - <dateTime1>, expressed as a 64 bit
     floating value.