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Forensic Science in Canadian Youth Courts

Updated: Sep 27, 2022

Most of the rules of evidence that apply to adults, also apply to proceedings in Youth Courts in Canada. Police officers can give evidence as to their observations, but experts are the only witnesses who can provide opinions, including opinions about forensic science. All forensic science, whether in adult court or Youth Court, involves measurement.

“[S]cience is measurement. If I cannot make measurements, I cannot study a problem scientifically.” — Dr. William H. George, Musical Acoustics Today, 16 NEW SCIENTIST 256, 256-57 (Nov. 1, 1962).

Gemologist's scale matching 10 paperclips agains a 5 gram mass. Measurement is a comparison
Measurement Implies Comparison: Ask the police "What compares with what?"

Sometimes forensic science measurements are done by police and sometimes they are done by scientists. If measurements are to be used for a forensic purpose, the measurements must be reliable.

What does it mean for a measurement to be reliable?

In order to understand reliability of forensic measurement used in Youth Court you need to think about the definition of "measurement". In Canada we have a federal law called the Weights and Measures Act. Section 4(1) of the Weights and Measures Act reads as follows:

"4 (1) All units of measurement used in Canada shall be determined on the basis of the International System of Units established by the General Conference of Weights and Measures."

So what is the International System of Units that we are required to use everywhere in Canada, including Youth Court, and where can we find out about it? The International System of Units is established by the General Conference of Weights and Measures. That is a rule in Canada because Canada is a member state of the Metre Convention. We use the International System of Units to express units of measurement because we are bound internationally by the Metre Convention. The main office of the General Conference of Weights and Measures, (Conférence générale des poids et mesures (CGPM)) is called the Bureau International des Poids et Mesures - the "BIPM". Their web site provides a lot of information about measurement.

Why, historically, do we have standard units of measurement that everybody in Canada is supposed to use? The answer is that Canada's legal history includes Magna Carta and the Constitution Act, 1867 which gave legislative authority to the federal Parliament to enact legislation respecting Weights and Measures. There is a similar provision in the US Constitution.

Here is what Magna Carta 1215 paragraph 35 says in Latin and in two English translations:

›"35. Una mensura vini sit per totum regnum nostrum, et una mensura cervisie, et una mensura bladi, scilicet quarterium Londoniense, et una latitudo pannorum tinctorum et russetorum et halbergettorum, scilicet due ulne infra listas; de ponderibus autem sit ut de mensuris."

›"35. Let there be one measure of wine throughout our whole realm; and one measure of ale; and one measure of corn, to wit, "the London quarter;" and one width of cloth (whether dyed, or russet, or "halberget"), to wit, two ells within the selvages; of weights also let it be as of measures."


›"35. There shall be standard measures of wine, ale, and corn (the London quarter), throughout the kingdom. There shall also be a standard width of dyed cloth, russet, and haberject, namely two ells within the selvedges. Weights are to be standardised similarly."

The concept of fair units of weights and measures goes back even further to many ancient texts:

Exodus 19: 35

"Your legal verdicts, your measures – length, weight, and capacity –must all be just. Your scales and weights must be just …"

Justice has a relationship with fair and standardized, weights and measures. There are obvious international commercial trade advantages to standardized weights and measures. It would make no sense, for example, in 1215 for the London standard width of cloth to be different than the York standard width of cloth. Notice in Magna Carta the reference to "una mensura", "one measure" in the whole realm. These days it is very important to have "one measure" for the whole world. Canada's measurements must be consistent with all international measurements. Justice and fair, standardized weights and measures, applies to trade but it also applies to all Court proceedings in Canada. I argue that this is a principle of fundamental justice protected by section 7 of the Canadian Charter of Rights and Freedoms.

This means that in order for the forensic science used in Ontario Youth Courts to be constitutional and in compliance with section 4(1) of the Weights and Measures Act, all measurements made by police or forensic scientists need to be made reliably and need to be made in relationship to the international standard units.

The point is that every measurement is a "comparison"(1). Every forensic measurement is a comparison. Every measurement used in Youth Court is a comparison. This is the case whether the measurement is referred to by a police officer, a forensic scientist, a lawyer, or a Judge.

Look at the image above. The scale, a gemologist's scale, is being used to compare the mass of 10 paperclips against a 5 gram mass. Grams are a unit of measurement derived from, 1/1000th of, the international standard unit of mass, the kilogram. The standard international kilogram that defines the meaning "kilogram", is a physical object that sits on a shelf in Paris, France. 2.

In looking at image of the gemologist's scale with paperclips, we can think about whether or not the scale is reliable, whether the scale is being used properly, whether the person using it knows how to use it, and most importantly whether the alleged 5 gm mass on the scale is really 5/1000ths of the physical kilogram object prototype in Paris. The latter issue is called "traceability" Traceability(1) is a big issue in forensic science, including the forensic science used in Youth Court.

Ask your Youth Court lawyer to research if the measurements relied upon by the Crown in proving its case against you are reliable and traceable.

1. See definitions of "measurement" and "traceability" in VIM: Joint Committee for Guides in Metrology, International Bureau of Weights and Measures,International Vocabulary of Metrology—Basic and General Concepts and Associated Terms (VIM)

2. Very recently the international definition of the kilogram has changed. See

See also:

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