Demo IOCs ioccircle and ioccircle together demonstrate PVA groups and links. ioccircle maintains a "phase" counter which counts from 0 to 359 then rolls over. From this phase are calculated an X and Y which are points on a circule with radius 1. A group PVA PV is defined which includes both and X and Y. ioccircle2 contains two calc records which subscribe to the X and Y from ioccircle and multiply each by 2. A second group PVA PV is defined including the multipled X and Y. Due to the atomicity of a group PV it is certain that pairs of X and Y will not be mixed. In this example, the magnitude sqrt(X*X+Y*Y) will never change by more than floating point epsilon.