We are sorry to hear that you are experiencing issues with our controls. I will try to briefly sum up and explain how the AutoRange and the ExtendDirection work.
The axis will work in either a auto mode or fully manual mode. If you set the AutoRange to true - you will have to set the min, max and step. It is not possible to set only the minimum and keep the automatic generated maximum (this is possible in the new ChartView
The ExtendDirection has little to do with the range. If the axis is in automatic mode (AutoRange = true) the axis would have calculated the range before the ExtendDirection property was taken into consideration. Say that the min was calculated to be 0, the step 20 and the max was calculated to be 80 (if the maximum value in the data was 79). If the ExtendDirection is Up - then the range would be extended to 100 (a reason for this could be to make place for the label "79"). If the ExtendDirection is None, then the auto range would not be extended and it would be 80 (with data max being 79).
You can try to set the IsZeroBased property and see if you get the behavior that you desire:
Alternatively you can iterate your data and find the data min and data max and build up the desired manual range. I hope this helps.
the Telerik team