The abbreviation stands for 230V Hand Held or Portable Class I sequence with no insulation (NI) test. This sequence would be used on 230V hand held or portable class I equipment that required a protective conductor current (aka earth leakage) measurement but not an insulation resistance test.
The factory set test sequences are shown on page 92 of the operating instructions. The table shows the factory set limits for each sequence. If a test is not included in a sequence the word "skip" will be shown in place of the limit to indicate that the test is "skipped" in that sequence.