Section 1252. Manner by which ratios shall be determined

In determining
  ratios pursuant to this article, the state board  shall,  for  the  last
  completed  assessment  roll  and  each  of the four preceding assessment
  rolls, determine the ratio of assessed valuation to full valuation as of
  the first day of January of the fiscal  year  for  which  the  ratio  is
  applicable.  Each  ratio  shall be determined on the basis of the market
  value survey completed pursuant to article twelve of  this  chapter  and
  for  which  the  valuation  date  is  the  first  day of January of each
  applicable year. In the event that a market value survey  has  not  been
  completed  based  upon  each  such valuation date, the state board shall
  determine the ratios in the following manner:
    (a) compute the ratio of assessed valuation to the full  valuation  of
  taxable  real  estate  on  the  basis  of market value surveys completed
  pursuant to article twelve of this chapter;
    (b) on the basis of the ratios computed pursuant to  subdivision  (a),
  project  increases  or  decreases  in the ratios for years for which the
  information has not been developed pursuant to article  twelve  of  this
  chapter;
    (c)  avail itself of appropriate market value information appearing in
  its office or acquired in the discharge of its duties pursuant  to  this
  chapter.