Не совсем понятно, что подавать на второй input plusMinusAverage в качестве значения атрибута до его изменения. Собственно, в этом и вопрос.
This node actually has different input attributes for use for different kinds of data. For simple numbers, you use the Input1D attribute and get the result from Output1D. For 2d attributes, such as UV coordinates, you use the Input2D attribute and get the result from Output2D. For 3d attributes, like vectors or colors or 3d coordinates, you use the Input3D attribute and get the result from the Output3D attribute.