They read the data capacitively. A sheet with perpendicular drive lines was put on top of the copper sheet. Energizing a drive line capacitively coupled to the

They read the data capacitively. A sheet with perpendicular drive lines was put on top of the copper sheet. Energizing a drive line capacitively coupled to the square capacitors on the BCROS sheet. Each bit had two capacitors (balanced), driving a differential amplifier (sense amplifier) to produce the output bit. Using two capacitors reduced noise since the differential amplifier would cancel out the noise.