PHP function calculate and display date time interval or time difference

This simple PHP function calculate and display's date time interval/difference of a two given value which is date time start/before and the current date time. This is useful when you want to display how old the record or articles in textual format.

<?
function calculate_time_ago($datefrom, $using_timestamps=FALSE){
    
	if (!$using_timestamps){
		$datefrom = strtotime($datefrom, 0);
	}// Convert time to timestamp
	
	$difference = (time() - $datefrom);// Difference in seconds
	
	if($difference < 60){ //1 second
		$rtnval = $difference." sec ago";
	} elseif($difference < 3600){ //1 hour
		$rtnval = round(($difference / 60), 0)." min ago"; 
	} elseif($difference < 86400){ //1 day
		$rtnval = round(($difference / 3600), 0)." hrs ago"; 
	} elseif($difference < 604800){ //7 days
		$rtnval = round(($difference / 86400), 0)." days ago"; 
	} elseif($difference < 2419200){ //4 weeks
		$rtnval = round(($difference / 604800), 0)." weeks ago"; 
	} elseif($difference < 31537800){ //365 1/2 days in 1 year
		$rtnval = round(($difference / 2419200), 0)." months ago"; 
	} elseif($difference > 31537800){ //365 1/2 days in 1 year
		$rtnval = round(($difference / 31537800), 0)." years ago"; 
	} else{ 
		$rtnval = "NA";
	}
	
	return $rtnval;
}
?>