I am sorry, this is probably very simple question related more to maths than blender itself, but I really have no idea what number respresents what angle. I have a feeling that it might be somehow related to euler or quaternion, or something like that (which I don't understand at all), but please, how do I know, what numerical value represents what rotation degree?
Let the picture speak for itself - it is located under driver dependencies (see the value of the driver in red circle). There is a value (which appereantly controls the value of the shape key), but I don't know what will the value be, when I rotate the bone by certain angle. So to make long story short: How to convert the angle in degrees to numerical value which is desired outcome to know the value of the shape key?