 Consider measuring the \(x\)-spin of a spin-½ system. Such a system will be found to be either “\(x\)-spin up” or “\(x\)-spin down”. Suppose that \(J\) is a good observer. For Everett, being a good \(x\)-spin observer meant that \(J\) has the following two dispositions (the arrows below represent the time-evolution of the composite system as described by the deterministic dynamics of rule 4a): 