Ok great! The reason they are both positive is that they are treated the same as e.g. the d-pad on a game controller, where each of the four directions are all positive in value. Same goes for the joysticks. You could argue the value should be a 2d vector in that case, but we went for consistency in the data types across input signals. The conversion from the signals to a 2d vector is also quite straightforward. 
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