A pilot tone generator receives optical energy from an optical communication medium carrying a plurality of optical signals. A terminal receives, from a base station, a zero-power channel state information reference signal indicator that indicates whether or not to estimate interference using a zero-power CSI RS signal, and, according to the zero-power CSI RS indicator, measures interference on the basis of the zero-power CSI RS. The method accesses the query plan and a set of stored intermediate statistics for records verified by query components, such as histograms that summarize the cardinality of the records that verify the query component. Vibration or oscillation effects inherent in the apparatus are compensated by the positioning, if necessary, of a counterweight. An electrical outlet receptacle block includes a series of outlet receptacles and connector sets selectively connectable to the further connector set of the junction block.