def METHOD_NAME():
    """Monitoring root API aims to query metrics history.
    Data are sorted by collect timestamp, in ascending order. By default, only
    the most fresh record set is returned. The query parameter 'start' can be
    used as lower bound and must be expressed as a UTC timestamp formatted
    using ISO8601 norm with a terminal 'Z' character. To limit the number of
    returned records to N, the query parameter 'limit' can be used and set to
    N. 'limit' default value is 50, meaning that the maximum number of record
    set this API returns by default is 50.
    """
    # Default values
    start_timestamp = None
    limit = 50
    app = default_app().temboard
    if 'start' in request.query:
        # Validate start parameter
        validate_parameters(request.query, [
            ('start', T_TIMESTAMP_UTC, False),
        ])
        # Convert it to epoch
        try:
            start_timestamp = (
                datetime.strptime(
                    request.query['start'], "%Y-%m-%dT%H:%M:%SZ"
                ) - datetime(1970, 1, 1)
            ).total_seconds()
        except ValueError:
            raise HTTPError(406, "Invalid timestamp")
    if 'limit' in request.query:
        # Validate limit parameter
        validate_parameters(request.query, [
            ('limit', T_LIMIT, False),
        ])
        limit = int(request.query['limit'])
    out = []
    h, n = app.config.temboard.home, 'monitoring.db',
    for _, metrics in db.get_metrics(h, n, limit, start_timestamp):
        metrics = json.loads(metrics)
        # Dropping current value, use /metrics to get them.
        db.drop_current_for_delta_metrics(metrics)
        out.append(metrics)
    response.set_header('X-TemBoard-Discover-ETag', app.discover.etag)
    return out