In product liability action alleging that ladder manufactured by defendant contained defective design that caused plaintiff to incur certain personal injuries, Dist. Ct. erred in allowing jury to examine exemplar ladder, which had been built to exact specifications of ladder used by plaintiff, that defendant’s expert used as demonstrative evidence during his testimony, where said ladder had not been introduced into evidence. Plaintiff objected to jury’s request to examine said ladder during jury deliberations, and as general matter, materials not admitted into evidence should not be sent to jury for use during its deliberations. Moreover, record showed that Dist. Ct. had originally overruled plaintiff’s objections to expert’s use of said ladder during his testimony, where Dist. Ct. noted that it would be used only for demonstrative purposes and would not be admitted into evidence. Instant error was not harmless since both parties had substantial evidence supporting their positions.