"rev counter" meaning in English

{
  "forms": [
    {
      "form": "rev counters",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "rev counter (plural rev counters)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        {
          "kind": "other",
          "name": "English entries with incorrect language header",
          "parents": [
            "Entries with incorrect language header",
            "Entry maintenance"
          ],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with 1 entry",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "other",
          "name": "Pages with entries",
          "parents": [],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Automotive",
          "orig": "en:Automotive",
          "parents": [
            "Transport",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        },
        {
          "kind": "topical",
          "langcode": "en",
          "name": "Measuring instruments",
          "orig": "en:Measuring instruments",
          "parents": [
            "Tools",
            "Technology",
            "All topics",
            "Fundamental"
          ],
          "source": "w"
        }
      ],
      "glosses": [
        "an instrument which displays the speed an engine is operating at in revolutions per minute (RPM)."
      ],
      "id": "en-rev_counter-en-noun-afcxq0hs",
      "links": [
        [
          "instrument",
          "instrument"
        ],
        [
          "revolution",
          "revolution"
        ],
        [
          "RPM",
          "RPM"
        ]
      ],
      "synonyms": [
        {
          "word": "tachometer"
        }
      ]
    }
  ],
  "word": "rev counter"
}

{
  "forms": [
    {
      "form": "rev counters",
      "tags": [
        "plural"
      ]
    }
  ],
  "head_templates": [
    {
      "args": {},
      "expansion": "rev counter (plural rev counters)",
      "name": "en-noun"
    }
  ],
  "lang": "English",
  "lang_code": "en",
  "pos": "noun",
  "senses": [
    {
      "categories": [
        "English countable nouns",
        "English entries with incorrect language header",
        "English lemmas",
        "English multiword terms",
        "English nouns",
        "Pages with 1 entry",
        "Pages with entries",
        "en:Automotive",
        "en:Measuring instruments"
      ],
      "glosses": [
        "an instrument which displays the speed an engine is operating at in revolutions per minute (RPM)."
      ],
      "links": [
        [
          "instrument",
          "instrument"
        ],
        [
          "revolution",
          "revolution"
        ],
        [
          "RPM",
          "RPM"
        ]
      ]
    }
  ],
  "synonyms": [
    {
      "word": "tachometer"
    }
  ],
  "word": "rev counter"
}