.Basic Table Calculation.
      TC cmd is , e.g., used to calculate elapsed time from timestamp
      data, summarize elapsed time then output average elapsed time.
      Operation +,-,*,/,% is available between 2 table columns.
      Summary supports subtotal by key-break or line-count.
      By column format function, data column is aligned by space delimiter,
      it enable to process data, e.g., vmstat output(unix cmd).
      See next section for sample usage.