Think Metric

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The Millimeter Standard War

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A 155 mm field gun used by the American Expeditionary Force in 1918

Using only millimeters for length measurements has the nice advantage that you don't need to specify units because everyone on a project knows that all lengths will be communicated in millimeters.  Sticking to exclusively millimeters, especially in engineering and manufacturing environments, reduces ambiguity and saves time.  Some call this practice the "Millimeter Standard" policy. 

If your shop has made the decision to go "Millimeter Standard", that's great.  However, "Millimeter Standard" in casual use can be rather cumbersome because of the unwieldy number of digits.  When headed to the local garden center to buy 20 meters of irrigation tubing, you probably don't want to be burdened with the 5-digit number 20,000. 

Most people find meters and centimeters quite practical for everyday measurements and only use millimeters when working with very small items.  On the other hand, if you prefer using millimeters for everything, go for it. 

Unfortunately, there are a number of vocal pseudo-experts out there Hell-bent on eradicating centimeters.  They consider centimeters unpure and unholy, but this stuborness impedes metrication.  Stay away from these pernicious crazies. 

Human Scale

A centimeter is the perfect precision for most "human scale" measurements.  For example, the imperial inch is too clunky to measure your height, and that's why a person's imperial height is often given to the 1/2 inch.  Use of millimeters for human height leads to false precision and awkwardly large numbers. 

Centimeters provide the correct level of precision and are super easy to communicate.  To answer an inquiry about your height, you just need to reply with a simple number, such as "184", and you're done. 

Long live the centimeter! 

Counterintuitive

Beleive it or not, a regular metric tape measure is better for "Millimeter Standard" work than a specialized millimeter only tape measure. 

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Big, bold, high-contrast scale

If you are measuring in millimeters on a regular metric tape measure, treat the numeric markers as the leading digits and the selected tick mark as the last digit.  For example, a reading of "7" concatenated with the 3rd tick mark means a measurement of 73 mm.  Rather than summing up the two components of the numbers, you're just gluing them together.  This technique is cognitively faster because it involves no math. 

Flawed Design

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Specialized millimeter only tape measure scale with tiny digits

Specialized millimeter only tape measures are based on a fundamentally flawed design because the last digit of every numeric marker is always useless.  The throwaway digit crowds the scale leading to reduced readability. 

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