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I have put a driver in the z rotation of an empty and made the variable a single property, where the path is the count in the array modifier.
My expression is 360/variable. I see that the driver value is as expected, but the rotation of the object is not like the driver value. Why this is happening and how can I fix it?

driver with wrong rotation value
The one with orange is right but the blue is wrong.

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    $\begingroup$ @someonewithpc that is not the problem at all, in fact that is not how drivers work. See my answer for what is going on here. $\endgroup$ – David Nov 8 '14 at 16:43
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That comes from the difference between degrees and radians. For some reason, the drivers evaluate rotation in radians no matter what the Units are set to in the Scene settings.

To get the expression working you have to convert radians to degrees. So your expression would be.
360/Array * 0.0174532925 or 360/Array * pi/180 or even shorter pi*2/Array

There are 0.0174532925 radians in 1 degree, so just multiply your expression by the difference between degrees and radians.

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  • $\begingroup$ Blender exclusively uses radians internally, so when working with the python api to manipulate internal values you have to use radians too. The scene setting just translates the units in the interface, AFAIK it doesn't do anything to the internal handling of units. $\endgroup$ – gandalf3 Nov 8 '14 at 20:18

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