Wis. Stat. § 906.02
A witness may not testify to a matter unless evidence is introduced sufficient to support a finding that the witness has personal knowledge of the matter. Evidence to prove personal knowledge may, but need not, consist of the testimony of the witness. This rule is subject to the provisions of s. 907.03 relating to opinion testimony by expert witnesses.
Wis. Stat. § 906.02
The chain of custody to items taken from the defendant's motel room was properly established although a police department laboratory chemist who examined the same was not present to testify when uncontroverted proof showed that the condition of the exhibits had not been altered by the chemist's examination, there was no unexplained or missing link as to who had had custody, and the items were in substantially the same condition at the time of the chemist's examination as when taken from defendant's room. State v. McCarty, 47 Wis. 2d 781, 177 N.W.2d 819 (1970). A challenge to the admissibility of boots on the ground that the victim did not properly identify them was devoid of merit, as it was stipulated that the child said they "could be" the ones she saw. Her lack of certitude did not preclude admissibility, but went to the weight the jury should give to her testimony. Howland v. State, 51 Wis. 2d 162, 186 N.W.2d 319 (1971).