You may specify the height of text and dimensions in drawing units, mm or inches. If the text height is specified in drawing units the text will be scaled in layouts. If the text height is specified in mm or inches then it becomes annotative text which is always drawn in the specified size on paper regardless of scale.
Make sure Simple Annotative Scaling
is enabled by selecting View Settings > Visibility
Text Height in drawing units
In the following example the text height is specified as 25 du (drawing units) for both text items and dimensions. The drawing scale as well as the layout scale is 1:10 and in the layout we have added 2 viewports at scales of 1:10 and 1:5 respectively.
Firstly the drawing:
And now the associated Detail layout with viewports at a scale of 1:10 (top) and 1:5 (bottom):
Notice that the text is scaled according to the viewport scale so that the text in the 1:5 viewport is twice the size of the text in the 1:10 viewport.
Text Height in mm or inches (annotative)
The following drawing is exactly the same except that the text height for both the text entity and the dimensions have been specified as 2.5mm.
Using mm or inches as the units tells AllyCAD and Civil Designer to print the text at a fixed size on paper regardless of scale.
Notice that the text and dimensions are printed at the same size of 2.5mm on paper regardless of the scale of the viewport.