Merge pull request #90 from nicoddemus/patch-2

Fix autoScale in scale_engine.py

Author: PierreRaybaut

qwt/scale_engine.py

@@ -674,10 +674,9 @@ def autoScale(self, maxNumSteps, x1, x2, stepSize):
             linearInterval = linearInterval.limited(LOG_MIN, LOG_MAX)
 
             if linearInterval.maxValue() / linearInterval.minValue() < logBase:
-                if stepSize < 0.0:
-                    stepSize = -math.log(abs(stepSize), logBase)
-                else:
-                    stepSize = math.log(stepSize, logBase)
+                # The min / max interval is too short to be represented as a log scale. 
+                # Set the step to 0, so that a new step is calculated and a linear scale is used.
+                stepSize = 0.0
                 return x1, x2, stepSize
 
         logRef = 1.0