title: Tensorboard v1.0 - Histogram tab interpretation
body: <p>I am learning to visualize tensor via tensorboard, however, I don't know how to interpret chart in Histogram tab. I used below code to visualize:</p>
  
  <pre><code>sess = tf.Session()
  tf.summary.histogram('test', tf.constant([1, 1, 2, 2, 3, 4, 4, 4, 4]))
  summary = tf.summary.merge_all()
  
  train_writer = tf.summary.FileWriter('../tmp/train', sess.graph)
  for i in range(10):
      sum = sess.run(summary)
      train_writer.add_summary(sum, i)
  </code></pre>
  
  <p>I got this chart from tensorboard:</p>
  
  <p><em>Histogram mode: offset</em>
  <a href="https://i.stack.imgur.com/OFLDz.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OFLDz.jpg" alt="enter image description here"></a></p>
  
  <p><em>Histogram mode: overlay</em>
  <a href="https://i.stack.imgur.com/DGIAB.jpg" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/DGIAB.jpg" alt="enter image description here"></a></p>
  
  <p>I know the x-axis is the value, y-axis is time step, what I don't know is the value of z-axis. According to <a href="https://github.com/tensorflow/tensorflow/issues/5381" rel="nofollow noreferrer">this</a> issue, </p>
  
  <blockquote>
    <p>It's a normalized density. I wouldn't describe it as a probability density,
    although I think calling it one would be justifiable.</p>
  </blockquote>
  
  <p>Can anyone explain more (i.e. how the density is calculated)?</p>