Member for - how Drupal 7 calculaties and formats duration?

Question

Drupal 7 has ability to show since how long someone is member, like this:

Member for 2 months 21 hours

What date field it uses to save the registration date/time? How it calculates and displays this duration? And can't we use same module / method to calculate duration from our date (in node) and display in our views?

I am really in need of this functionality of calculating of duration, I am using views Calc and subtracting end-date from start-date and dividing it with number of seconds in day to get number of days between two days. but not satisfy besides don't know why can't subtract now() from a given date field in views calculations.

Answer 1

$account->content['summary']['member_for'] = array(
  '#type' => 'user_profile_item',
  '#title' => t('Member for'),
  '#markup' => format_interval(REQUEST_TIME - $account->created),
);

It's in function user_user_view($account). And yes, of course you can use format_interval($interval) function in other places.