Clock skew is the difference in insertion delay between the destination clock path and the source clock path. You measure it from their common point in the design to the endpoint and startpoint sequential cell clock pins, respectively.
In the equation Tskewi,j = Tcj- Tci, Tcj and Tci are defined as follows:
- Tcj
- The delay from the common node to the endpoint clock pin.
- Tci
- The delay from the common node to the startpoint clock pin.