function dateAdd( start, interval, number ) {
	
    // Create 3 error messages, 1 for each argument. 
    var startMsg = "Sorry the start parameter of the dateAdd function\n"
        startMsg += "must be a valid date format.\n\n"
        startMsg += "Please try again." ;
		
    var intervalMsg = "Sorry the dateAdd function only accepts\n"
        intervalMsg += "d, h, m OR s intervals.\n\n"
        intervalMsg += "Please try again." ;

    var numberMsg = "Sorry the number parameter of the dateAdd function\n"
        numberMsg += "must be numeric.\n\n"
        numberMsg += "Please try again." ;
		
    // get the milliseconds for this Date object. 
    var buffer = Date.parse( start ) ;
	
    // check that the start parameter is a valid Date. 
    if ( isNaN (buffer) ) {
        //alert( startMsg ) ;
        return null ;
    }
	
    // check that an interval parameter was not numeric. 
    if ( interval.charAt == 'undefined' ) {
        // the user specified an incorrect interval, handle the error. 
       //alert( intervalMsg ) ;
        return null ;
    }

    // check that the number parameter is numeric. 
    if ( isNaN ( number ) )	{
       // alert( numberMsg ) ;
        return null ;
    }

    // so far, so good...
    //
    // what kind of add to do? 
    switch (interval.charAt(0))
    {
        case 'd': case 'D': 
            number *= 24 ; // days to hours
            // fall through! 
        case 'h': case 'H':
            number *= 60 ; // hours to minutes
            // fall through! 
        case 'm': case 'M':
            number *= 60 ; // minutes to seconds
            // fall through! 
        case 's': case 'S':
            number *= 1000 ; // seconds to milliseconds
            break ;
        default:
        // If we get to here then the interval parameter
        // didn't meet the d,h,m,s criteria.  Handle
        // the error. 		
        //alert(intervalMsg) ;
        return null ;
    }
    return new Date( buffer + number );
}