Rules and scales used in measurement in the forensic setting: measured—and found wanting!

Abstract

The need for accurate measurement of marks, injuries or scars, and of objects, implements or weapons, in a criminal or forensic setting is paramount, as such measurement may identify evidentially important links between a mark, injury or scar, and an object, implement or weapon, which in turn may result in linking these to an individual or excluding an individual from involvement in a crime. If accurate measurements are not undertaken, that opportunity may be lost. The absence of a readily available ruler scale with an integral colour chart led to the development of a new design (http://www.forensigraph.com) whose measured scale was compared with a tape measure (http://www.fisco.co.uk) of an EC Class II standard which regulates quality of increment printing on the blade and temperature tolerances (i.e. the blade will not expand/contract in normal temperature ranges) and whose length measures correspond with the articles and essential requirements of EC Directive 2004/22/EC and its annex MI-008. This tape measure was also used to compare standard clear plastic 600 and 1200 Helix rules (http://www.helix.co.uk) bought via retail outlets on the high street in the UK. Both Forensigraph and clear plastic and stainless steel rules were consistent in measurement with the EC Class II standard measure (Fig. 1). A major UK police service circulated a pdf file of a paper rule for use by police personnel and healthcare professionals for printing off and using in the forensic and healthcare settings for wound and other object measurement. This rule had been sourced via a web search at http://www.vendian.org/mncharity/dir3/paper_rulers/. The website clearly stated when printing off this rule ‘disable any ‘‘shrink to fit’’ option when printing’. That instruction had not been included with the circulated paper rule. Comparison of this paper rule as circulated and printed off with the Forensigraph and the standard clear and stainless steel Helix rules showed that the paper based rule was substantially inaccurate, with a true 600 length being measured as 6.500 on the paper based rule or almost 1 cm different at 10 cm. As this had clear potential implications for the accuracy the police service were advised to withdraw it from use. The reason for the inaccuracy was that the size of the printed-out rule was dependent on the page set-up of the printer, which in turn could vary between police stations and between departments within each station. Because of the large number of commercially available printers it is not possible to assess whether, if the ‘shrink to fit’ setting is disabled, all printers will produce accurate rules. A series of Epson printers (Epson Stylus Photo PX650, Epson Stylus SX 215, Epson Stylus DX 8400, and Epson Stylus PX810 FW) produced accurate printouts, but other models and printers from other manufacturers may not. Accurate forensic scales are appropriate for photography and imaging of injuries, scars and other marks, particularly where patterns may be evident. Good quality images can support or enhance medical records or assist with the physical fit of an injury to an object, implement or weapon J. J. Payne-James Cameron Forensic Medical Sciences Barts and The London School of Medicine and Dentistry, Charterhouse Square, London EC1M 6BQ, UK