Hello!
I am using this javascript for smooth scroll to the desired item on the main page. I can not solve 2 problems:

1. Two menu (Menu Item a Type: External URL) contains external anchor links and look like this: #about_us.
Added to the scrollable element anchors <div id="about_us">
When you click on a menu item script works and moves in the right place, but because of internal links (for example from another menu item with article) does not go back.
2. It is impossible to calibrate scrolling. It turns or less than you need to scroll or higher.
Please help me )