As soon as you select a dimension for editing, AutoCAD Mechanical toolset displays the Power Dimensioning ribbon contextual tab. This contextual tab displays the properties of the selected dimension and provides the means to change them.
For example, you can tag a dimension as a reference dimension, by simply clicking a button on the ribbon. You can also choose to display the dimension text in alternate units, again at the click of a button on the ribbon. You can set the precision for primary units and secondary units independently, by specifying the number of decimals in a text box on the ribbon.
You can add fits or tolerances to the dimension and choose the representation from a list. You can also control the precision of fits and tolerances, independently of the precision of the dimension value. The drafting standard controls text sizes for the deviation automatically, eliminating the need for additional dimension styles.
When the PICKFIRST system variable is turned on, you can select more than one dimension for editing. When multiple dimensions are selected, the contextual tab shows the value of the properties that have the same value across all the selected dimensions. The properties that are different are indicated to be in a mixed state. For example, the linear scale box, displays the scale as a numeric value. If the linear scale is different across the selected dimension, the linear scale value is shown as "VARIES". If you change the value of a property, the change is applied across all selected dimensions.
When the PICKFIRST system variable is turned off, you must run the AMDIMMEDIT command and then select the dimensions to edit.
AutoCAD Mechanical toolset does not permit editing of dimensions on locked layers.