title: Customizing and understanding GnuRadio QT GUI Vector Sink
body: <p>I have created a simple GnuRadio flowgraph in GNU Radio Companion 3.8 where I connect a Vector Source block (with vector [1,2,3,4,5]) to a QT GUI Vector Sink.  When I run the flowgraph, I see a two lines:  one which goes from 1 to 5 (as expected) and one which is perfectly horizontal at zero.  If I set the reference level in the sink to something other than zero (e.g., 1), that line at zero remains (in addition to a line at the reference).  Additionally, the legend in the upper right corner contains Min Hold and Max Hold buttons.  An example is shown below:</p>
  
  <p><a href="https://i.stack.imgur.com/RdU7h.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/RdU7h.png" alt="enter image description here"></a></p>
  
  <p>I have a few questions:</p>
  
  <ol>
  <li>What is this line at zero?  How do I get rid of it?</li>
  <li>How do I get rid of the Min and Max Hold options in the upper right of the plot?</li>
  <li>In general, is it true that finer control of the formatting of plots in GNURadio is possible when explicitly writing code (say in a python-based flowgraph) to render the plot instead of using companion?</li>
  </ol>