setBatchMode(true);
  imageSize = 512;
  slices = 6;
  nTries=40;
  maxThreads=30;
  threads=newArray(nTries);
  times=newArray(nTries);
  saveThreads = call("ij.Prefs.getThreads");
  for (i=0; i<nTries; i++) {
     showProgress(i,nTries-1);
     nThreads=1+round((i/(nTries-1))*(i/(nTries-1))*(maxThreads-1)); // more attempts with lower n
     call("ij.Prefs.setThreads", nThreads);
     newImage("Untitled", "32-bit random", imageSize, imageSize, slices);
     t1=getTime();
     run("Median...", "radius=2 stack");
     t2=getTime();
     threads[i] = nThreads;
     times[i] = t2-t1;
     close();
  }
  setBatchMode(false);
  Plot.create("Median times", "Number of threads", "time(ms)", threads, times);
  call("ij.Prefs.setThreads", saveThreads);