When working at a smaller scale (ie. 1/8th"), make it so the duct center lines always appear the same size. The duct center lines are drafting tools only and do not appear on the drawing therefore having them adjust with the DIMSCALE is not neccesary. When the DIMSCALE is changed to 96 or higher, drafting in tight spaces can be difficult when the duct centerlines are large because the arrows are too large to work with and tend to overlap others.