27. During the course of the hearing much was made of the fact that under Section 73 the Responsible Authority may only amend a permit if it is satisfied that among other things the amendment will not cause an increase in detriment to any person, and the concept of detriment is not qualified by words such as material or substantial. Here we are not dealing with Section 73 and it is considered that the concept of the consequences of any amendment vis-à-vis purpose of the control is a more useful way of looking at the discussion. Nevertheless, it is useful to observe that the idea of increased detriment should be based on the ability of an ordinary person to perceive or discriminate change. For example, if a 3 metre wall is proposed in a boundary, and a 4.5 metre wall is built in its place, any reasonable person would readily perceive a change. On the other hand, if a 3 metre wall is proposed and a 3.1 metre wall is built, most people could not discern the change without the aid of a measuring device. In making this observation it is important to recognise that many people may accept in the abstract the idea of a 3 metre wall being built on the boundary, and are then shocked at the outcome of the construction. However, this does not change the fact that the difference between a 3 metre wall and a 3.1 metre wall is not perceivable. The affected person is concerned by the reality of the wall which is in the order of 3 metres high, and not by the 100mm difference between that which was approved and that which was constructed.