Well, if I add

Qt Code: 
  1. plot.replot();
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right before all the invTransform() functions the console outputs:

Qt Code: 
  1. invTransform():  1.97826
  2. invTransform():  1.97826
  3. invTransform():  1.96078
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It should output a five. Those 1.9something looks to me like the lowerBound...