We consider an appeal from the judgment entered in Appellee’s favor in a products liability action. Following the denial of post-trial motions and judgment, an appeal to this Court was filed in which a panel of this Court affirmed the trial court. We have granted reargument, however, for three principal reasons:
1. to clarify the role which “state of the art” evidence, including evidence of industry custom and federal safety standards, plays within the context of a strict liability action;
2. to re-examine the rule which prohibits hearsay statements appearing in learned treatises and other informational material from being admitted into evidence and used as substantial proof of the matters to which they relate; and,
3. to determine the admissibility of evidence of similar prior accidents to show constructive, post-sale notice of a defective product.
The underlying facts of this case are as follows. On April 20, 1978, Appellant-Henry Majdic (Majdic) was employed by National Standard Company. Majdic’s duty on that date was to operate a power press which was designed, manufactured, and sold by Appellee-Cincinnati Machine *615Company (Cincinnati). The power press was utilized to perform various functions in conjunction with the punching, stamping, bending, or sheering of metal. In operating the press, Majdic hand fed sheet metal between the dyes attached to the ram and bed of press, which shaped and formed the metal.1 The procedure entailed further steps which necessitated Majdic to reach into the machine to remove the work in process at least ten times. The power press, however, was not equipped with a guard to prevent an operator’s hands from coming in contact with the point of operation. Likewise, no safety feature was attached to bar the operation of the press while the user’s hands were between the ram and bed. No warning signs were posted on the machine advising of the danger involved in exposing one’s hands to the point of operation.
On the date in question, the ram of the power press descended upon Majdic’s right hand as he operated the machine. Thereafter, on April 8, 1980, Majdic and his wife, Ann, commenced an action against Cincinnati, the manufacturer of the power press, for the injuries he received from the accident. Three theories of recovery were asserted: negligence, breach of implied and expressed warranties, and strict liability. The action, however, was tried solely on the strict liability theory. By his complaint, Majdic contended that Cincinnati had manufactured and sold the press in a defective condition. This averment was based on the Restatement (Second) of Torts § 402A.
It was Majdic’s position at trial that the power press was defectively designed inasmuch as it did not contain a guard which would have prevented the operator’s hands from entering the point of operation. In addition, Majdic claimed that the machine was defective since it was not equipped with a mechanism to prevent operation of the press while the user’s hands were in the pinchpoint. Further, the lack of a warning of the danger involved in placing one’s hand in *616the work area was cited as a ground for the claim of defective design.
During the course of trial, Cincinnati did not dispute Majdic’s allegation that the power press had not been equipped with guards and warnings discussed, supra. Rather, Cincinnati maintained that the press brake was a general purpose, multifunctional unit which was unequipped with dies and had no point of operation when sold. Thus, Cincinnati claimed that only Standard Machine Company, which incorporated the press brake into its manufacturing system, could determine and install the guards and warnings necessary for the particular function assigned to the press. (Appellant’s Brief, 12). Cincinnati posited that, for this reason, the responsibility for providing the guards and warnings rested solely with Standard Machine Company, Majdic’s employer. The verdict returned by jury was in Cincinnati’s favor. Majdic filed a Motion for a New Trial which contained assignments of error allegedly committed by the trial court in its evidentiary rulings.
Before beginning an analysis of the evidentiary rulings involved, it is important that we remain mindful of the broad and sound social policy which underlies a seller’s liability as established by the Restatement (Second) of Torts, § 402A. Section 402A provides:
(1) One who sells any product in a defective condition unreasonably dangerous to the user or consumer or to his property is subject to liability for physical harm thereby caused to the ultimate user or consumer, or to his property, if (a) the seller is engaged in the business of selling such a product, and (b) it is expected to and does reach the user or consumer without substantial change in the condition in which it is sold.
(2) the rule stated in Subsection (1) applies although (a) the seller has exercised all possible care in the preparation and sale of his product, and (b) the user or consumer has not bought the product from or entered into any contractual relation with the seller.
*617The social policy sought to be effected by the implication of the seller’s liability is very basic, very simple and very sound. As between an innocent user of a product and a manufacturer or seller who is engaged in the business of manufacturing or selling a product, risk of loss for injuries resulting from the use of a defective product shall be borne by the manufacturer and/or seller. Salvador v. Atlantic Boiler Co., 457 Pa. 24, 319 A.2d 903, 907 (1974). See: Webb v. Zern, 422 Pa. 424, 220 A.2d 853 (1966) (§ 402A adopted as the law of Pennsylvania).
With this guiding principle in mind, one can readily analyze the application of liability under § 402A. In a product liability case, principles of negligence have no place. Dambacher By Dambacher v. Mollis, 336 Pa.Super. 22, 27, 485 A.2d 408, 428 (1984). Liability does not focus upon a manufacturer’s reasonableness in the design or manufacture of the product. Nor does it concern the manufacturer’s use of “state of the art” concepts. Rather, liability rests where there is a defect in the product which caused injury to the user. Whether or not the defect was known or could have been anticipated at the time of the design or manufacture is of no concern. Id.
Section 402A does contain the term “unreasonably dangerous,” which arguably introduces negligence concepts into products liability cases. However, our Supreme Court has explained that that term was included within § 402A “to foreclose any argument that the seller of a product with inherent possibilities for harm would become ‘automatically responsible for all the harm that such things do in the world.’ ” Berkebile v. Brantly Helicopter Company, 462 Pa. 83, 95, 337 A.2d 893, 900 (1975) (quoting Prosser, Strict Liability to the Consumer in California, 18 Hast.L.J. 9, 23 (1966)). Later, in Azzarello v. Black Brothers Co., Inc., 480 Pa. 547, 391 A.2d 1020 (1978), the term “unreasonably dangerous” was found to impose on the trial court the responsibility of determining “as a matter of law and by resolving considerations of ‘social policy’, whether ‘the risk of loss should be placed upon the supplier.’ ” Dambacher, *618supra, 336 Pa.Superior Ct. at 59-60, 485 A.2d at 426 (quoting Azzarello, supra, 480 Pa. at 556, 391 A.2d at 1025). We now consider the propriety of the evidentiary rulings challenged by Majdic on appeal.
I. “State of the Art” Evidence
We are mindful that questions concerning the admission and exclusion of evidence are vested within the trial court’s discretion. Absent an abuse, of that discretion, such rulings will not be reversed. Burch v. Sears, Roebuck and Co., 320 Pa.Super. 444, 456, 467 A.2d 615, 621 (1983). In assessing the propriety of the trial court’s actions, a fundamental consideration in determining the admissibility of evidence is its relevance. Evidence is relevant if it tends to make a fact at issue more or less probable. Martin v. Soblotney, 502 Pa. 418, 422, 466 A.2d 1022, 1024 (1983).
Over Majdic’s objection, Joseph L. Schwalje was permitted to testify concerning the custom in the industry in 1949 with respect to power press brakes. Cincinnati sold the press which injured Majdic to National Standard Machine in 1949. The witness testified that it was customary practice at that time for an employer or another party implementing the press brake into a metal forming system to provide the necessary safety devices. Further, Schwalje was permitted to refer to the 1973 American National Standards Institute (ANSI) Safety Standards for power presses to demonstrate that the standard in 1973 was the same as the trade custom prevalent in 1949.
At trial, Majdic argued that evidence of industry practices or trade customs was inadmissible in strict liability cases since it related to the reasonableness of a manufacturer’s conduct. The trial court rejected this argument and found the testimony to be relevant as to whether the press brake was defective at the time it was sold to National Standard. The written 1973 ANSI reports were excluded from evidence; however, Schwalje was permitted to refer to them in order to determine the industry custom during 1949.
Recently, our Supreme Court in Lewis v. Coffing Hoist Division, Duff-Norton Co., Inc., 515 Pa. 334, 528 A.2d 590 *619(1987), considered the identical issue presented by Majdic— the admissibility of custom and usage as well as industry standards in a products liability case. In Lewis, the plaintiff was injured while using a control box to operate an overhead hoist. The plaintiff stumbled and struck one of the control buttons, causing the overhead hoist chain to disengage, swing forward, and hit both of his legs. During trial, the trial court admitted the plaintiffs evidence that if the control box had been designed in a different fashion, the accident would have been prevented. The defendant attempted to put into evidence a publication of the American Society of Mechanical Engineers, which set forth standards with respect to the manufacture of electric hoists and other industrial lifting equipment. Likewise, the defendant sought to introduce evidence by an expert witness that at least ninety percent of the electric hoists manufactured in this country had control panels devoid of safety guards around the activating buttons. Both types of evidence were excluded by the trial court on grounds that such evidence injected into the case concepts of negligence. On appeal the Superior Court upheld the trial court’s ruling and our Supreme Court affirmed.
In this bellwether decision, the Pennsylvania Supreme Court noted that there existed a general consensus among the various jurisdictions that the manufacturer’s due care has no bearing in a products liability case. However, there is a discrepancy among the courts with respect to the relevance and admissibility of evidence demonstrating industry standards, customs and practices of the design of products. Id., 515 Pa. at 342, 528 A.2d at 593. After embarking upon an analysis of the treatment of such evidence among our sister states, the Lewis court opined:
[hjaving reached the conclusion that evidence of industry standards relating to the design of the control pendant involved in this case, and evidence of its widespread use in the industry, go to the reasonableness of the appellant’s conduct in making its design choice, we further conclude that such evidence would have improperly *620brought into the case concepts of negligence law. We also conclude that such evidence would have created a strong likelihood of diverting the jury’s attention from the appellant’s control box to the reasonableness of the appellant’s conduct in choosing its design. For those reasons we conclude that the trial court correctly ruled the evidence to be irrelevant and hence inadmissible.
Id., 515 Pa. at 343, 528 A.2d at 594. (Emphasis supplied).
Further, the Concurring Opinion of Mr. Justice Larsen adds:
[t]he injection of industry standards into a design defect case would be not only irrelevant and distracting, but also, because of the inherently self-serving nature of ‘industry standards’, would be highly prejudicial to the consumer/plaintiff. By our determination today, we have made it clear that a manufacturer cannot avoid liability to its consumers that it injures or maims through its defective designs by showing that ‘the other guys do it too.’
Id., 515 Pa. at 344, 528 A.2d at 595.
We are aware that there exists in Pennsylvania cases which have discussed, and even suggested, that custom or usage and state of the art, as well as similar matters, should be admissible in design/defect cases. It is abundantly clear that the rationale employed in this body of cases has been expressly rejected by Lewis. Likewise, to the extent that the dicta in the recent panel decision of this Court in Foley v. Clark Equipment Co., 361 Pa.Super. 599, 523 A.2d 379 (1987) seems to suggest that a change in the law in this area would be desirable, we disapprove of that language.
For the reasons cited above, we reverse the trial court’s decision to admit into evidence testimony concerning the custom in the industry during 1949 as it related to power brakes. Further, we hold that the trial judge improperly permitted evidence of the 1973 ANSI Safety Standards for power presses. Accordingly, we must remand this case for a new trial.
*621II. The Use of Learned Treatises
At trial, Majdic presented the expert testimony of Paul Glasgow, a mechanical engineer, who testified that in his opinion the power press manufactured by Cincinnati had been defective because of the absence of safety guards. During Glasgow’s testimony, Majdic sought to introduce into evidence various articles from trade publications and learned treatises which Glasgow had relied upon in forming his opinion. He also offered as evidence numerous patents which suggested the availability of safety guards at the time the power press had been manufactured. Although the trial court permitted Glasgow to refer to these materials, it refused to allow them to be received into evidence or their contents to be read to the jury.
The law in this Commonwealth is well-settled that an expert witness may be cross-examined on the contents of a publication upon which he or she has relied in forming an opinion, and also with respect to any other publication which the expert acknowledges to be a standard work in the field. See: Cummings v. Borough of Nazareth, 430 Pa. 255, 242 A.2d 460 (1968); Walheim v. Kirkpatrick, 305 Pa.Super. 590, 451 A.2d 1033 (1982); and, Brannan v. Lankenau Hospital, 254 Pa.Super. 352, 385 A.2d 1376 (1978), rev’d, on other grounds, 490 Pa. 588, 417 A.2d 196 (1980). In such cases, the publication or literature is not admitted for the truth of the matter asserted, but only to challenge the credibility of the witness’ opinion and the weight to be accorded thereto. Brannan v. Lankenau Hospital, supra, 254 Pa.Superior Ct. at 365, 385 A.2d at 1383. Learned writings which are offered to prove the truth of the matters therein are hearsay and may not properly be admitted into evidence for consideration by the jury. See: McCormick on Evidence § 821, at 899 (3d ed. 1984).
Under the current state of the law in this Commonwealth, it was entirely proper for the trial court to refuse to admit into evidence the treatises and patents offered by Majdic. Because these materials were being offered to *622prove the truth of the matters asserted therein (i.e., that safety guards could have been added to the press in 1949), they were hearsay, and were inadmissible as substantive evidence. It was also proper for the trial court to refuse Majdic’s offer to allow his expert witness to read the contents of the documents aloud in court. Excerpts from a publication which are read into evidence for the purpose of proving the truth of the statements contained therein are still hearsay and, therefore, inadmissible. This fact is not changed merely because the document is read into evidence by the witness instead of being received as an exhibit for inspection by the jury. It is the purpose for which the information is offered, not the manner in which is introduced, which makes it objectionable.
Majdic concedes that information contained in private treatises is hearsay. Nevertheless, he argues that we should adopt a more liberal view towards treatises and periodicals and allow their admission when relied upon by an expert. That decision, however, is not for this Court to decide; therefore, we decline this invitation.
With respect to the patents, the learned treatise exception has no application. The assurances of trustworthiness which are intrinsic in scholarly treatises do not exist where patents are concerned. Unlike learned treatises, patents are not necessarily propounded by an expert in the field in which the patent applies; rather, they may be obtained by any individual with an original idea. Moreover, they are not generally subject to the type of criticism and analysis which learned treatises usually undergo. In light of these circumstances, the trial court did not abuse its discretion either by refusing to admit the treatises and patents into evidence or by declining to allow portions thereof to be read to the jury.
III. Prior Accidents
Majdic argues that the trial court erred by refusing to admit into evidence certain admissions by Cincinnati concerning 64 accidents that involved injuries to operators of *623its press brake. All of these incidents occurred prior to Majdic’s accident. This evidence was sought to be introduced to prove that Cincinnati was aware of the dangerous propensities of the machine, but did not warn of the dangers involved. The trial court disallowed this evidence and ruled that Majdic had failed to show that the prior accidents had occurred under similar circumstances to Majdic’s incident.
It is established in this Commonwealth that a “defective condition” is not limited to defects in the design or manufacture of a product. The test is whether or not the product is equipped with every element necessary to make it safe for use. Berkebile v. Brantly Helicopter, supra, 462 Pa. at 100, 337 A.2d at 902. In Berkebile, our Supreme Court noted:
[o]ne such element may be warnings and/or instructions concerning use of the product. A seller must give such warning and instructions as are required to inform the user or consumer of the possible risks and inherent limitations of his product. Restatement (Second) of Torts § 402A, comment h. If the product is defective absent such warnings, and the defect is a proximate cause of the plaintiff’s injury, the seller is strictly liable without proof of negligence.
Id., 462 Pa. at 100, 337 A.2d at 902.
A product’s “defective condition” may be proven through circumstantial evidence such as the occurrence of similar accidents. Cornell Drilling Co. v. Ford Motor Co., 241 Pa.Super. 129, 139, 359 A.2d 822, 827 (1976). Evidence of similar accidents occurring at substantially the same place and under the same or similar circumstances is generally admissible to prove a manufacturer’s constructive notice of a dangerous or defective condition.2 However, the admis*624sion of such evidence is tempered by judicial concern that the evidence may raise collateral issues which confuse both the real issue and the jury. These matters are vested within the sound discretion of the trial court. Whitman v. Riddell, 324 Pa.Super. 177, 182, 471 A.2d 521, 523 (1984). To constitute reversible error, a ruling on evidence must be shown to be erroneous and harmful to the complaining party. Id., 324 Pa.Superior Ct. at 180, 471 A.2d at 521, quoting Anderson v. Hughes, 417 Pa. 87, 208 A.2d 789, 791 (1965).
During trial, Majdic sought to introduce into evidence certain admissions made by Cincinnati in reference to 64 accidents involving the same type of press brake which had injured him. Majdic’s purpose in requesting the introduction of this evidence was to show that the mere occurrences of the 64 accidents served as notice to Cincinnati of the dangerous propensities of the unshielded press brake and that Cincinnati had the duty to alert those who used the machine to these dangers. In addition, Majdic maintained that the specifics of these accidents were unnecessary in presenting these admissions to the jury. The trial court disagreed, however, and ruled that the admissions were repetitious and lacked the required specificity as to whether the accidents were in fact similar to the circumstances under which Majdic was injured. We have reviewed the record of the instant case and find that the trial court did not err by excluding Majdic’s proffered evidence. The admissions, as presented to the trial court, specified neither the exact circumstances under which the other accidents occurred nor in what manner they were similar to Majdic’s accident. Clearly, the burden with respect to the admissibility of prior accidents was not sustained by Majdic. Therefore, we find that the trial court did not abuse its discretion in disallowing the admissions.
As pointed out, supra, Cincinnati conceded during trial that it had been aware of the hazards associated with the *625use of the power press. Cincinnati argued, though, that since the power press was utilized as a component part of National Standard’s larger metal forming system, the machine did not become dangerous until after it had been integrated. Therefore, National Standard, the buyer, was responsible for installing the necessary safety features and warnings commensurate to the particular function the power press served. Cincinnati essentially maintained that it could not be charged with the duty of apprising each buyer of the product’s inherent dangers, given the wide array of purposes for which the machine was utilized.
We disagree. Although Cincinnati may have indeed expected its buyers to correct any safety hazards associated with the power press once it was consolidated within their manufacturing systems, a manufacturer’s duty to warn of the dangers may nevertheless continue when it becomes cognizant that its buyers are not making the necessary safety adjustments to its product. It would be a question of fact for the jury to determine whether the product was safe absent sufficient instructions to its purchasers that safety guards and warnings should be attached to the power press upon implementation into a larger metal forming system. For this reason, we believe that on retrial it would be appropriate to permit Majdic to introduce evidence of similar accidents so that Cincinnati’s claim that it was unnecessary to inform its buyers of the product’s hazards after integration may be challenged. However, we emphasize that in order for such evidence to be admissible, it must be comprised of similar accidents occuring at substantially the same place and under the same or similar circumstances.
IV. Cross Examination of Richard Griesheimer
During trial, Cincinnati presented testimony of Richard Griesheimer, a staff engineer and former manager of engineering. On cross-examination, Majdic attempted to cross-examine Mr. Griesheimer concerning the discrepancy between answers to interrogatories which had been filed in *626this case by Cincinnati and those which it had filed in a case in another jurisdiction. In the instant case, Cincinnati answered that it had no knowledge of injuries, other than Majdic’s, resulting from the use of its power presses. By comparison, Cincinnati had filed answers to interrogatories in another action in which it listed approximately 60 separate incidents involving the power press, including Majdic’s claim. Majdic attempted to use these inconsistencies to impeach Cincinnati’s credibility on cross-examination.
“It is well-established that the scope and limits of cross-examination are within the trial court’s discretion and the court’s rulings thereon will not be reversed in the absence of a clear abuse of discretion or an error of law.” Kemp v. Qualls, 326 Pa.Super. 319, 324, 473 A.2d 1369, 1371 (1984). After considering Majdic’s arguments in support of the requested cross-examination, the trial court refused this line of questioning in light of its previous ruling which excluded evidence of prior accidents. The trial court opined that the materiality and relevance of the cross-examination would be outweighed by its resulting prejudice to Cincinnati.
We conclude that the trial court erred in prohibiting this line of questioning which went to Cincinnati’s credibility. The totally different answers filed in the other action by Cincinnati were a proper subject matter for cross-examination on the issue of credibility. We find that the trial court could have restructured the questioning to ensure that the jury would not focus its attention on extraneous issues in light of the trial judge’s previous ruling. Thus, we find that the trial court abused its discretion on this evidentiary matter.
The judgment is reversed. Case remanded for a new trial consistent with this Opinion.
WIEAND, J., files a dissenting opinion. OLSZEWSKI, J., files a concurring and dissenting statement.. The ram was the mobile upper part of the machine, while the bed was the stationary lower part of the press.
. Although there exists in Pennsylvania neither statutory nor case law on point discussing a manufacturer’s post-sale duty to warn, we note that a trend has developed among our sister states which places such a duty on a manufacturer. See Allee, Post-Sale Obligations of Product Manufacturers, 12 Fordham Urb.LJ. 625 (1984) (collecting cases); and, Royal, Post Sale Warnings: A Review and Analysis Seeking Fair *624Compensation Under Uniform Law, 33 Drake L.Rev. 817 (1983) (collecting cases).