def get_index_value(self, y):
            return min(1.0, max(0.0, 1.0 - float(y-1)/(self.control.height-1)))
Add an arbitrary charge or credit to a customer's account.  A positive
dataset/ETHPy150Open enthought/mayavi/tvtk/util/tk_gradient_editor.py/FunctionControl.Channel.get_index_value--crossover with--dataset/ETHPy150Open SeanOC/sharpy/sharpy/product.py/Customer.charge