21.1. For the allocation of senators by the principle of proportional representation referred to in the second paragraph of article 56 of the Constitution, the pure proportionality formula will be used in accordance with the following rules:
a) The total cast votes for the election of senators by the principle of proportional representation is understood as the sum of all votes placed in the ballot boxes for the national multi-member regional electoral district list, and
b) The allocation of senators by the principle of proportional representation will be done considering as the national cast votes that which remains after deducting all votes in favor of the political parties that failed to receive three percent of the vote for the corresponding list, the invalid votes, the votes for unregistered candidates and the votes for Independent Candidates from the total votes cast.
21.2. The pure proportionality formula has the following elements:
a) Natural Quotient, and
b) Largest remainder.
21.3. Natural Quotient: is the result of dividing the national cast votes by the number of seats to be distributed for senators elected by the principle of proportional representation.
21.4. Largest Remainder: is the highest remainder between the remaining votes cast for each political party, once the allocation of seats is done by the natural quotient. The largest remainder is used when there are still seats left to distribute.
21.5. For the application of the formula, the following procedure will be observed:
a) By the natural quotient, each political party will be allocated as many senators as the number of times that its votes contain the natural quotient, and
b) After applying the natural quotient, if there are still seats to be divided, these will be allocated using the largest remainder method, following the descending order of the remaining not used votes for each of the political parties.
21.6. In any case, in the allocation of senators by the principle of proportional representation, the order that the candidates had in the national list will be followed.