PER CURIAM.

Defendant was convicted by a jury of fourth-degree criminal sexual conduct, MCL 750.520e; MSA 28.788(5), for engaging in sexual relations with his 20-year-old mentally retarded daughter. Defendant appeals as of right.

A motion in limine was filed by defendant prior to trial wherein he alleged that his daughter was incompetent to testify. After examining the victim, the court agreed that, despite her apparent ability to tell the truth, the victim's limited mental ability and her susceptibility to influence made her incompetent as a witness. See MRE 601. The court further held, however, that pursuant to People v Edgar, 113 Mich. App. 528; 317 N.W.2d 675 (1982), the transcript of the victim's preliminary examination testimony could be read to the jury.

Defendant's first argument on appeal, that the trial court abused its discretion by ruling the victim incompetent, is without merit. Defendant cannot request a certain action in the trial court, in this instance a finding that the victim was incompetent, and then, after the request has been followed by the court, argue on appeal that the action was error. People v Murry, 106 Mich. App. 257, 262; 307 N.W.2d 464 (1981).

Defendant next argues that the trial court erred in allowing the victim's preliminary examination testimony to be admitted into evidence.

MRE 804(b)(1) provides that the prior testimony of a witness is admissible in a subsequent proceeding if the witness is unavailable to testify and if the party against whom the testimony is offered had an opportunity and similar motive to develop the testimony of the witness at the prior hearing. See also MCL 768.26; MSA 28.1049. We find that the trial court correctly ruled under MRE 804(a)(4) that the victim, due to her mental incapacity, was unable to testify and was therefore unavailable as a witness. Further, the transcript of the preliminary examination shows that defendant utilized his opportunity to develop the victim's testimony on the issue of his guilt by cross-examination. Therefore, we find that, despite contrary findings by the examining magistrate and the trial court on the issue of the victim's competency, the preliminary examination transcript was properly allowed into evidence. Edgar, supra, p 535. Any inconsistency goes to the weight of the evidence, not its admissibility. Edgar, supra.

The next issue raised by defendant involves a tape recording of a conversation between the victim and her brother, the prosecution's main witness, made after the alleged assault but prior to police involvement. The existence of the tape contradicted the brother's testimony at the preliminary examination that he had not discussed the incident with his sister before he reported it several days later to the sheriff's department. By this, defendant intended to show that the brother had improperly influenced his sister's thinking with regard to the assault by discussing it with her before she was questioned by the police. The court ruled that the contents of the tape would not be admissible unless defendant opened the door by using the tape to impeach the brother's testimony. Defendant did not attempt to impeach the victim's brother by use of the tape. Defendant argues that the court's ruling violated the "best evidence" rule as the best evidence of a conversation is not a tape recording of the conversation, but rather the testimony of the conversants. We do not agree. First, the best evidence rule generally applies only where the contents of documentary evidence are in dispute. People v Trudeau, 51 Mich. App. 766, 772; 216 N.W.2d 450 (1974), lv den 391 Mich. 839 (1974). See People v Manier, 19 Mich. App. 602, 605; 173 N.W.2d 248 (1969). Second, even if the best evidence rule were applicable here, we would rule that, once a proper foundation was established, see People v Frison, 25 Mich. App. 146; 181 N.W.2d 75 (1970), the tape recording would be more reliable than the memory of one or both of the conversants as to what was actually said.

Defendant further contends that the tape recording would have been inadmissible hearsay. However, had defendant made mention of the tape in an effort to show that the victim's brother had improperly influenced her story, the tape would have been admissible by the prosecutor in rebuttal under an exception to the hearsay rule. People v Davis, 106 Mich. App. 351, 354-355; 308 N.W.2d 206 (1981), lv den 414 Mich. 947 (1982).

Defendant's final argument on appeal is that the trial court prejudiced his case by treating defense counsel in a derogatory fashion. We have carefully reviewed each instance brought to our attention and conclude that the conduct of the court did not deny defendant a fair and impartial trial. Jackson v Depco Equipment Co, 115 Mich. App. 570, 582; 321 N.W.2d 736 (1982).

Affirmed.