In CAD systems, the integration of parametric functionalities can provide practical benefits. This is evident in AutoCAD. In this paper, a bidirectional constraint implemented in AutoCAD is understood as a constraint between variables such that when any one variable changes, the other variables involved are automatically adjusted by AutoCAD to maintain the constraint.

Based on the rich set of equality and inequality relations in planar geometry, it is possible to construct a library of base blocks. Each base block contains a geometric figure that realizes a specific constraint among the lengths of certain Line objects. This paper presents a method for supplementing AutoCAD with commands to coordinate the base functions, which automatically insert the necessary base blocks, decompose the resulting objects, and add supplementary constraints. As a result, it is possible to ensure the desired bidirectional constraints in the form of equalities or inequalities of the lengths of Line objects in the drawing.

Additionally, there are commands to manage the created constraints, such as displaying the symbolic form of the constraint, identifying the participating objects, and removing constraints. The described method is also useful when a complex constraint can be replaced by a system of constraints available in AutoCAD, along with the types of constraints introduced here.