138.100.  Rules — hearings (first classification counties). — 1.  The following rules shall be observed by such county boards of equalization:

  (1)  They shall raise the valuation of all tracts or parcels of land and all tangible personal property as in their opinion have been returned below their real value; but, after the board has raised the valuation of such property, notice shall be given that said valuation of such property has been increased and a hearing shall be granted; such notice shall be in writing and shall be directed to the owner of the property or the person controlling the same, at his last address as shown by the records in the assessor's office, and shall describe the property and the value thereof as increased; such notice may be by personal service or by mail and if the address of such person or persons is unknown, notice may be given by publication in two newspapers published within the county; such notice shall be served, mailed or published at least five days prior to the date on which said hearing shall be held at which objections, if any, may be made against said increased assessment;

  (2)  They shall reduce the valuation of such tracts or parcels of land or of any tangible personal property which, in their opinion, has been returned above its true value as compared with the average valuation of all the real and tangible personal property of the county.

  2.  Such hearings shall end on the thirty-first day of July of each year, except in any city not within a county or any county with a charter form of government, in which such hearings shall end by the fourth Saturday in August; provided, that the estimated true value of personal property as shown on any itemized personal property return shall not be conclusive on the assessor or prevent the assessor from increasing such valuation.  Provided further that said board of equalization may meet thereafter at least once a month for the purpose of hearing allegations of erroneous assessments, double assessments and clerical errors, and upon satisfactory proof thereof shall correct such errors and certify the same to the county clerk and county collector.

  3.  The board of equalization in all counties with a charter form of government shall provide the taxpayer with written findings of fact and a written basis for the board's decision regarding any parcel of real property which is the subject of a hearing before any board of equalization.

  4.  The provisions of subsection 3 of this section shall only apply in any county with a charter form of government with more than one million inhabitants.