Mr. williamson has a link at the top to the tutorial on using transformation constraints.
“Or you might be able to do it with the transformation constraint: http://cgcookie.com/blender/lessons/3-final-rigging-transformation-constraint/9”
In this lesson he builds a rotating needle that rotates based on the translation of a control object.
Object Constraints: Transformation. This lesson builds one.
You just have to change the shape. Create a needle- move the origin to the end you want the needle to rotate on. Create the object you want to use to control the rotation. Link the needle to the control object with a “transformation object constraint” as he does in the video. Translate-source-location into destination-rotation. Set the axis rotation min and max in degrees.
