  Studies of the response of the SiD silicon-tungsten electromagnetic
calorimeter (ECal) are presented. Layers of highly granular (13 mm^2 pixels)
silicon detectors embedded in thin gaps (~ 1 mm) between tungsten alloy plates
give the SiD ECal the ability to separate electromagnetic showers in a crowded
environment. A nine-layer prototype has been built and tested in a 12.1 GeV
electron beam at the SLAC National Accelerator Laboratory. This data was
simulated with a Geant4 model. Particular attention was given to the separation
of nearby incident electrons, which demonstrated a high (98.5%) separation
efficiency for two electrons at least 1 cm from each other. The beam test study
will be compared to a full SiD detector simulation with a realistic geometry,
where the ECal calibration constants must first be established. This work is
continuing, as the geometry requires that the calibration constants depend upon
energy, angle, and absorber depth. The derivation of these constants is being
developed from first principles.
