9. The system of claim 1 , wherein the processor is to aggregate output signals from a plurality of viewers.
9. The system of claim 1 , wherein the processor is to aggregate output signals from a plurality of viewers. 10. The system of claim 9 , wherein the calculator is to calculate at least one of a maximum, a minimum, an average, a deviation, a derivative, an amplitude or a trend of at least one parameter of the output signals to aggregate the output signals.