= Solution
For independent contributions the parametrization means
$$
\boxed{\sigma^2(E)=A^2E+B^2+C^2E^2.}
$$
The <Statistical fluctuation>[stochastic] coefficient $A$ includes fluctuations in the sampled <Electromagnetic shower>[shower] fraction, the finite number of signal quanta, and intrinsic <Electromagnetic shower>[shower] fluctuations. A number of detected quanta proportional to $E$ has fluctuations proportional to $\sqrt E$, giving relative resolution proportional to $E^{-1/2}$. The <noise> coefficient $B$ describes an approximately fixed energy-equivalent readout uncertainty, including <electronic noise> and, for specified running conditions, <Collision pileup>[Pile-up] contributions. The constant term $C$ represents residual fractional nonuniformity, <Calorimeter calibration>[calibration] and response variations, imperfect correction for inactive material, and leakage effects over the fitted range. The simple three-term model is an approximation; leakage and <Collision pileup>[Pile-up] need not follow these powers exactly.
A <homogeneous calorimeter> uses the showering material itself as the active medium, for example a <Scintillator>[scintillating crystal]. It removes the absorber-versus-active sampling fluctuation and can have a much smaller <Statistical fluctuation>[stochastic] term, but it does not eliminate <Poisson distribution>[signal statistics] or intrinsic <Electromagnetic shower>[shower] fluctuations. Its <noise> and constant terms are not automatically smaller: they depend on light collection, <Calorimeter calibration>[calibration], temperature, radiation damage, electronics and geometry. <Homogeneous calorimeter>[Homogeneous detectors] can offer excellent <energy> resolution and compact construction, but large crystal volumes can be costly and fine longitudinal segmentation difficult. <Sampling calorimeter>[Sampling detectors] often provide economical large coverage and flexible segmentation with robust <Sampling calorimeter>[absorbers], at the cost of sampling fluctuations and inactive material. If <energy> is expressed in GeV, $A$ has units $\mathrm{GeV}^{1/2}$, $B$ has units GeV and $C$ is dimensionless.
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