Fractional impact of the most important sources of systematic uncertainty on the total uncertainty of the signal strength, for (top) the MSSM signal hypothesis of m<sub>A</sub>=500 GeV, tan&beta;=20, (bottom) the Z<sup>&prime;</sup><sub>SSM</sub> signal hypothesis of m<sub>Z<sup>&prime;</sup></sub>=1.75 TeV. For each source of uncertainty, F<sub>&plusmn;</sub> = &plusmn;&sigma;<sup>2</sup><sub>source</sub> / &sigma;<sup>2</sup><sub>total</sub> is defined as the positive (negative) fractional contribution to the signal strength uncertainty.