There are several tabs for dimensioning elements in which you can define how elements on different Faces or directions should be dimensioned.
In each tab, you can choose from different options. Some of them may vary depending on Category chosen:
Horizontal Dimensions/ Vertical Dimensions - choose options for vertical and horizontal dimensions
Measure Width/Position - turns ON Horizontal/Vertical dimensioning
Measure - choose to where dimension point should snap
Location Point - will snap to insertion point of Family
Location Line - will snap to location line. Available for line-based elements (Structural Framing, Pipes, etc.).
Left/Right Edge - will snap to the edges of solid body in the Family
Reference planes - will snap to reference planes which are inside Family. Reference planes should be set to Left/Top/Center etc.
Model lines - will snap to model lines, which are inside Family. Model lines should be perpendicular to dimension line string in the view.
Join Dimension Lines - if OFF, each element will have its own dimension line. That's why it's usually ON, to have fewer dimension strings.
Measure Only First & Last Element - will skip dimensioning of intermediate elements
Disconnect from Total Dimension Point - will give dimension only between measured elements
Dimension Position - select from available options where to place them
Left/Right/Top/Bottom - dimensions will be placed at selected side, outside of all elements, to be included in Total Measure
By Element - dimension will be placed at nearest side
By Measure - dimension will be placed at position of dimensioned element
Text Note - enter value for text note. Works with Text Note Settings. (See relevant help file.)
Text Note Parameter - select parameter, which should be added as a note to the dimension line. Works with Text Note Settings. (See relevant help file.)
Grouping - group dimension lines by selected parameter of elements on selected Face.