title: Overlaying or merging multiple .ps files
body: <p>I have used gmt to create several .ps files of x - y graphs with identical axes. I have several sets of data, each containing between 14 and 20 plots. Each plot is in a separate directory.</p>
  
  <p>I would like to overlay every .ps within a dataset, in order to show correlation between the plots.</p>
  
  <p>I know this is similar to the thread posted here: </p>
  
  <p><a href="https://stackoverflow.com/questions/501723/overlay-one-pdf-or-ps-file-on-top-of-another">overlay one pdf or ps file on top of another</a></p>
  
  <p>but I don't have to deal with multiple pages.</p>
  
  <p>I'm not a programmer, I'm a student! I would really appreciate a quick-ish way to stack them on top of each other to see an overall trend.</p>
  
  <p>If not, I'm off to buy a stack of OHP films and find the nearest photocopier.... which would not look nearly as shiny.</p>
  
  <p>All help is appreciated!</p>