You can specify sketch dimensions using equations instead of discrete values. The equations solve automatically as you drag the sketch geometry.
To use equations to specify dimensions, double-click a dimension in a sketch and in the Modify dialog box, start the equation by typing = (equal sign). You can also enter a Global Variable, Function, or File Property from the flyout menu.
Sketch equations are listed in the Sketch View
of the Equations, Global Variables, and Dimensions dialog box. Click to display the dialog box.
You can also edit sketch equations in the Equations dialog box to create custom constraints.