jQuery one pagescrolling

jQuery one pagescrolling

Hi all ... I have created a menu. When I click on it it scroll down to see the specific div ... but how to stop on accurate place ... for example at the top line of the div .. or 20px under this line ... u know what I mean? I hope yes ... please help me ... thanks a lot 

... I download something but I am not sure if it is whole code 

  2. <script>
  3.             if ( ! window.console ) console = { log: function(){} };

  5.             // The actual plugin
  6.             $('.single-page-nav').singlePageNav({
  7.                 offset: $('.single-page-nav').outerHeight(),
  8.                 filter: ':not(.external)',
  9.                 updateHash: true,
  10.                 beforeStart: function() {
  11.                     console.log('begin scrolling');
  12.                 },
  13.                 onComplete: function() {
  14.                     console.log('done scrolling');
  15.                 }
  16.             });
  17.         </script>