title: Slider to choose numbers between -24 and 24 with 0.5 step
body: <p>I want to create slider that gives to the user an ability to choose numbers on a range of -24 to 24 with 0.5 steps. 
  So that, I decided to create slider whose thumb is located at the center and could be slided to both left and right sides. Here's the picture of what I am aiming at:
  <a href="http://i.stack.imgur.com/7SiMs.jpg" rel="nofollow">thumb is located at the center and user can move it to both sides</a></p>
  
  <p>When user moves the thumb of slider to the left it sets negative numbers. Similarly, when user moves it to the right it sets positive numbers.</p>
  
  <p>How can I achieve this? 
  Is there another better way to give a user such ability?</p>