title: d3 zoom behavior. Increasing the scale in small increments
body: <p>In d3 zoom behavior, for linear scale, how can I gradually increase the zoom. I use it like</p>
  
  <pre><code>var zoom = d3.behavior.zoom()
      .x(x)
      .y(y)
      .scaleExtent([1, 10])
      .on("zoom", zoomed);
  </code></pre>
  
  <p>If I understand correctly, the chart will zoom up to 10x. Is it like, each double click will zoom it 1x times, till it reaches 10x? How can I make it even finer step like, 1, 1.2x, 1.4x,..</p>
  
  <p>Thanks.</p>