query: #title: Check units
  # Complex constraint from [[Property talk:P2610]]
  # Unit must to be a [[d:Q1978718|unit of length <small>(Q1978718)</small>]]
  SELECT ?item ?unit
  WHERE {
    ?item p:P2610/psv:P2610/wikibase:quantityUnit ?unit.
    MINUS {
      ?unit wdt:P31 wd:Q1978718.
    }.
  }