I apologize for the confusion. Based on the information provided, it appears that you are trying to install a dishwasher in a space with a width of 450 units, but the designer is stating that you need a space of 500 units to properly install the dishwasher. It's possible that the designer is correct and a space of 500 units is needed for proper installation, but it's also possible that they are recommending a larger space due to other factors such as ease of installation or access for maintenance. Without more information about the specific dishwasher model and the layout of the space in question, it's difficult to say for certain.