title: Getting correct axis sub-divisions when zooming in D3
body: <p>I am wondering how to approach creating the ticks for a zoomable chart that represents musical information. </p>
  
  <p>I would like to have a chart with 4 ticks [0-1-2-3-4] on the X Axis that as it is zoomed will sub-divide each tick in half to give [0-0.5-1-1.5-2-2.5....] then half again to give [0-0.25-0.5-0.75-1...] and so on.</p>
  
  <p>The current default behaviour seems to be to divide between integers first by half, then into fifths.</p>
  
  <p>Is it possible to achieve this behaviour using a function or would I need to set the ticks manually taking into account the scale and transform values of my chart?</p>
  
  <p>Thanks</p>