What is the test for certifying that a notary has "personal knowledge" of an individual?

The notary in Anderson v. Aronsohn, supra, 181 Cal. 294, 184 P. 12, took the acknowledgment of three different individuals. As to the first two, the notary relied upon an introduction under oath by a third person personally known to him, made in connection with another transaction. Thereafter the notary met them five or six times on social and business occasions before certifying that they were known to him. As to the second individual, the notary was introduced to her by his former teacher. He met her on another occasion before acknowledging her signature. The court held that under these circumstances the notary did not have the requisite degree of acquaintance with the three individuals to certify that he possessed "personal knowledge" of them. The court stated the test of such knowledge as follows: "Such knowledge ... involves such an acquaintance, derived from association with the individuals in relation to other people, as establishes their identity with at least reasonable certainty. Such an acquaintance cannot in its very nature depend upon the mere word of one or two or three individuals, but must be based upon a chain of circumstances surrounding the person in question, all of which tend to show that they are what they purport to be. That there is nothing to arouse suspicion is not enough." (181 Cal. at p. 297, 184 p. 12.)