Register number. Each register has 5 values (ES/SES/UAS/CV/LOSWS). The 15 minute history has 32 history registers, indexed from 1 to 32. Each accumulates its measures over 15 minutes. The register with index 1 is the oldest register (numerical equals chronological order). The 15 minute history has an additional entry (index 33) for the current register (which is only updated when perfControlUpdatePeriod of the associated perfControlEntry is not zero). The 24 hour history has 7 true history registers, indexed 1 to 7. These accumulate there measures over 24 hours. Again, the register with index 1 is the oldest, and again, there is a current register with index 8. This current register is updated every 15 minutes, no matter what the value of perfControlUpdatePeriod of the associated perfControlEntry is.