Try using the following:
The same thing does not happen with DecimalUpDown.
<xctk:DoubleUpDown AllowSpin="True"
FormatString="F16"
Increment="0.01"
Minimum="0.0"
Maximum="1000.0"
MouseWheelActiveOnFocus="True"
SelectAllOnGotFocus="False"
ShowButtonSpinner="True"
TextAlignment="Right"
Margin="8,0"
Grid.Column="1"
HorizontalAlignment="Left"
Focusable="False"
MinWidth="100"/>
If you keep pressing one of the buttons, after a while the actual value increase slightly differs from the Increment value. Is this expected? I thought double values have 15-16 digits accuracy.The same thing does not happen with DecimalUpDown.