Every cell has multipletiming arcs. For example, a combinational logic cell, such as and, or, nand, nor, adder cell, has timing arcs from each input to each output of the cell. Sequential cells such as flip-flops have timing arcs from the clock to the outputs and timing constraints for the data pins with respect to the clock. Each timing arc has a timing sense, that is, how the output changes for different types of transitions on input. The timing arc ispositive unate if a rising transition on an input causes the output to rise (or not to change) and a falling transition on an input causes the output to fall (or not to change).

In a non-unate timing arc, the output transition cannot be determined solely from the direction of change of an input but also depends upon the state of the other inputs. For example, the timing arcs in an xor cell (exclusive-or) are non-unate.

Unateness is important for timing as it specifies how the edges (transitions) can propagate through a cell and how they appear at the output of the cell.