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Internally we work with metric units and use decimal fractions for sub units, e.g. 1cm or 0.35cm or 23mm)

We're building a user oriented design tool for laying out reports and was wondering what the most most common approach taken by UI developers who are still working in Imperial measurements (Inches etc.) when it comes to decimalised fractions.

Most of my cultural references point to people using 1/2, 1/4, 1/8 or 1/32 inch when measuring fractions. But when faced with decimal equivalent what do people tend to do?

For example do people use 0.5, 0.25, 0.125 etc or do you people roll these up to say 0.5, 03, and 0.1 inch?

Edit: I'm really more concerned about people who use software to lay out pages for display as opposed to laying out real world items such as blueprints or construction plans.

Sorry for the confusing question.

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migrated from Oct 24 '13 at 1:34

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3 Answers 3

The preferable way to display this is a fraction. It is a very common form of display that anyone in the United States who has held a tape measure will find (be it for fabric or construction).

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If one is to use a decimal rather than a fraction, it should be shown to to the two or three digits of accuracy. If one reads "1.3" inches and understands this to be a rounded value, it may be 1/3 or it may be 1/4 - it can't be sure (these are important differences when tight tolerances are needed - doing some home improvement, 1/16th of an inch (less than 0.1) is what the tolerances are often needed).

This means that 1/4 is to be shown as 0.25, 1/8 as 0.125, and 1/16th as 0.063. People who are familiar with working with the fractions often have the decimal values of fractions of the power of 2 (at least for 2, 4, and 8) (1/2, 1/4, 3/4, 1/8, 3/8, 5/8) memorized. Many times they will be familiar with and able to recognize the decimal representations of n/32 too.

In woodworking shops where one gets decimal values from digital tools (calipers, laser range finders), it isn't uncommon to see a table of fractions to decimal form such as:

enter image description here

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So in essence you're saying that people who are used to the task will likely use memorised exact values as opposed to rounded values? – Preet Sangha Oct 24 '13 at 5:10
@PreetSangha To me, it read as 'concerning measurement: america is bananas and should be ignored'. Ditto for dates :D. DPI is amongst the most terrible of afflictions upon the world. – Gusdor Oct 24 '13 at 10:31
@PreetSangha Correct. Where imperial measurements with tight tolerances are needed, rounded values can be ambiguous. I'm not a pro woodworker, but with the amount I have done, I can tell you all the n/8 fractions from memory (as can my mother from her work with fabric). In metalwork (where its even less forgiving), I know people who can do the 16ths from memory and can tell you the 32nds without too much thought. As a caveat, you might find people using decimal inches (1.1, 1.2, 1.3) in graphic work though, though they likely also know the exact fractional values too. – MichaelT Oct 24 '13 at 14:18

It's not very common to use inches for lengths in screen layouts. I imagine if inches are being used it's more for rough sketching, so terms like "7 3/4 inches" is more easily understood (by those used to inches) than "7.8 inches" and is close enough.

It's more common to use metric units, points (1/72 inch), pixels or reference pixels (1/100 inch), font based units (ems and rems) or percentages of the available screen.

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As a foreigner who has worked with both metric and imperial systems, as well as with design applications made by American companies (photoshop, quark, etc), I would say it is OK to continue using fractions instead of their decimal equivalent.

The reason is that most users using those applications use (or used) the US/English version, which has trained them in the use of fractions - to the point that fractions have become the standard notation, even for people living in countries using the metric system.

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