Hi
You can set property dimensions, as well. Click right mouse button on icon's tool or on already existing dimension and from local menu select "Properties / Format," and here you can set the size of the arrowheads and font size. You can also set your text style and dimension style by the "Tools / Palettes / Style Manager Palettes / Style Dimensions (I'm not sure if this is in the free version) and there set the arrows and text size, and use them for dimensioning. See snaps.