P.R. Laws tit. 10, § 1086
In order to graduate the weight of evidence of books of merchants, the following rules shall be observed:
(1) Books of merchants shall be evidence against themselves, no proof to the contrary being admitted; but the opponent can not accept the entries which are favorable to him and reject those which prejudice him; but, having admitted this means of evidence, he shall abide by the result which they may show in their entirety, taking into equal consideration all the entries relating to the matter in litigation.
(2) If the entries of the books exhibited by two merchants should not conform, and those of one of them have been kept with all the formalities mentioned in §§ 1071—1087 of this title and those of the other contain any defects or lack the requisites prescribed by this Code, the entries of the books correctly kept shall be admitted against those of the defective ones, unless the contrary is demonstrated by means of other proofs legally admissible.
(3) If one of the merchants should not present his books or should state that he does not possess any, those of his adversary, kept with all the legal formalities, shall be evidence against him, unless it is proven that the lack of said books is caused by force majeure, and always reserving the evidence against the entries exhibited, by the other means legally admissible in suits.
(4) If the books of the merchants possess all the legal requirements and are contradictory, the judge or court shall determine by the rest of the evidence, classifying it according to the general legal rules.
History —Commerce Code, 1932, § 41.