Cal. PROB § 21503

(a) If an instrument includes a formula intended to eliminate the federal estate tax, the formula shall be applied to eliminate or to reduce to the maximum extent possible the federal estate tax. (b) If an instrument includes a formula that refers to a maximum fraction or amount that will not result in a federal estate tax, the formula shall be construed to refer to the maximum fraction or amount that will not result in or increase the federal estate tax.