In all cases where duties are levied on the basis of an estimated declaration by the parties, the declaration and the estimate must be detailed.
A declaration of this nature shall, before the execution of the registration, the merged formality or the land publicity formality, be subscribed, certified and signed at the foot of the document to be formalised, where the sums or values to be used as a basis for the proportional or progressive duty are not determined therein.
Failing this, the formality shall be refused.