forces the dimension units to be centered between the dimension endpoints. Deselect the Center Text button to position the dimension units manually.
The Center Text button
forces the dimension units to be centered between the dimension endpoints. Deselect the Center Text button to position the dimension units manually.
Hold CTRL while drawing a dimension line to force the opposite state of the Center Text button. For example, holding CTRL when the Center Text button is deselected turns on the text centering constraint.
The Angle Constraint button 
forces dimension lines to draw only in 15-degree increments.
Hold SHIFT while drawing a dimension line to force the opposite state of the Angle Constraint button. For example, holding SHIFT while the Angle Constraint button is selected turns off the constraint.