It is possible that persons may be disqualified from serving as witnesses on grounds not expressly enumerated in codes of evidence or by general common law principles -- on unenumerated grounds such as age, illness, sensory defects, defects in intelligence, lack of understanding, inability to communicate, defects in memory, and inability to be truthful.

Fed. R. Evid. 102 ("These rules shall be construed to secure...elimination of unjustifiable...delay" as well as other matters and purposes.).Avoidance of waste of time and undue delay influences and constrains the law of evidence and the process of proof in litigation.

Cf. Amoco Production Co. v. United States, 619 F.2d 1383, 1391 (10th Cir. 1980) (plaintiff filed an action to quiet title to the disputed mineral rights, alleging that the Utah recording statutes provided them with constructive notice of....A duplicate is a counterpart produced (a) from the same impression as the original; (b) from the same matrix; (c) by means of photography, including enlargements and miniatures; (d) by mechanical or electronic re-recording; (e) by chemical reproduction; or (f) by equivalent techniques that accurately reproduce the original.

Cf. Luther v. Maple, 250 F.2d 916, 921 (8th Cir. 1958) (personal injury and property damage action arising out of an automobile accident; district court entered judgment upon a jury verdict in favor of plaintiffs; defendant asserted that the district court erroneously admitted into evidence...A trial court has absolute discretion or close to absolute discretion to reject visual and demonstrative evidence.