253.56. The variation in the taxable value of a unit of assessment is established by comparing the value entered on the roll on the day of coming into force of the roll with the value that was entered on the preceding roll on the preceding day.
For the purposes of the first paragraph, the value subtracted or added pursuant to an alteration made to the roll, on or before its coming into force, under any of paragraphs 6 to 8, 12, 18 and 19 of section 174 shall not be taken into account, except if a corresponding alteration was made to the preceding roll.
Where a unit, on the roll coming into force, results from the combination of several whole units that appeared on the preceding roll on the preceding day, the sum of the taxable values of the units shall be considered to be the taxable value entered on the preceding roll of the unit resulting from the combination.