The code in the top right does the following. It applies the current roll angle as an extra roll delta in the opposite direction to return the roll to center, The value in the clamp function sets when the return force activates because for values less than its threshold it will be v - v, but for values greater than its threshold it will be 45 - v which will then apply a delta to keep the roll at 45 degrees. It was a simple way to virtually lock the roll to a set range. Adjusting the return force by changing the divisor will change how much it will fight you, and setting the clamp value to a smaller range will make it correct roll at a sooner angle. If you replace the output of the clamp function with a constant zero, it will return to zero.