Use the Job preferences dialog (the Codes / Units tab) to define the units for all objects drawn using the options available in Autodesk AutoCAD Structural Detailing. Units are selected for reinforcement length, reinforcement cover, reinforcement diameter, etc.
While working in Autodesk AutoCAD Structural Detailing, you may adopt different work units (mm, cm, and m). The default model scale is 1: 20. All descriptions of bars and bar distributions as well as dimensions will be inserted in the default scale. The default scale may be changed in the lower part of the Object Inspector dialog.
It is possible to work in several scales at the same time using active views. To do this, create a few views and define an appropriate scale for them, e.g.: 1:20, 1:25 or 1:50.
To draw objects in the scale, e.g. 1:50, activate the view with this scale (it will be highlighted in red) and insert reinforcing bars (the scale of their description will be 1:50). The scale of an active view is set on the Model tab.
The scale of a drawing presented in a selected view, may be changed by modifying the scale. Scale modification includes description of reinforcement distribution, dimension lines, texts and line scale (ltscale) of reinforcement description; once this option is selected, a drawing presented on the Model tab displays the changes (size of letters, labels and dimension lines). When views created in different scale are inserted into a printout layout, the size of fonts and dimension lines are identical.
For more information see the following topics:
Different scale of drawings in a view and preparation of printout.