Awad, I. A., A. - E. Gawad, and A. M. Soliman,
"Simplified formulas for $Δ$$ømega$/$ømega$ and $Δ$Q/Q based on Budak-Petrela's method",
Circuits and Systems I: Fundamental Theory and Applications, IEEE Transactions on, vol. 42, no. 3: IEEE, pp. 186–187, 1995.
Abstract