 defining 
    dx and dy the finest grid size in x and y direction is given, defaulting to 
    one half of electrode spacing. The values nx and ny denote for each layer, 
    how big the cells are, in multiples of dx and dy, respectively.
</td><td>
    <p align=center><img src="pic/paramod.png" width="518" height="236"></p>
</td></tr></table>
<h3><a name="free"></a>Free model edit</h3>
<p>For setting up whole volumes to distinct resistivities the following dialog 
  is useful.</p>
<p align=center><img src=