title: Django and units conversion
body: <p>I need to store some values in the database, distance, weight etc.<br>
  In my model, I have field that contains quantity of something and <code>IntegerField</code> with choices option, that determines what this quantity means (length, time duration etc). </p>
  
  <p>Should I create a model for units and physical quantity or should I use <code>IntegerField</code> that contains the type of unit? </p>