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Comment by sandworm101 | Hacker News Reader

Forget the stats and calculus. Think carpentry, measuring and cutting wood products. If you are building things in the US/UK/Canada then you are using feet and inches. 12 inches to a foot. It's a tiny thing to learn and will serve kids well in any number of professions.

Now 11, that's a total mystery. Other than it being between 10 and 12, I see no reason to memorize 11s.

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11s are practically free, though, in base 10. The algorithm "repeat the non 11 number twice" works up till 10 x 11, where the "add a 0" algorithm for 10 kicks in. So you're just really memorizing 11 x 11 = 121 and 11 x 12 = 132.

A simple trick: For 11 x a 2-digit number you can simply take the first digit of the 2-digit number then the 2 digits of the number added together then the last digit of the 2-digit number.

Ex: 11 * 12 = 132 or 1, 1+2, 2. 11 * 45 = 495 or 4, 4+5, 5. For numbers which sum to more than 10 add the carry to the first number ex: 11 * 59 = 649 or 5, 5+9 = 14 so add 1 to the initial 5 and keep the 4, 9.

I'm 29 and never heard this before. Neat!

This is golden: I am just over 40 and I now know that I knew nothing at 29!

This generalizes to multiplying any number times 11,

https://en.wikipedia.org/wiki/Trachtenberg_system#Multiplyin...

Take a number, say 142857. Prepend a 0 on the left. Underneath each digit write the sum of the digit above and the one to the right. If you work from the right, it's easier to keep track of the carries.

  0142857
  1571427

But it's also "practically free" to just mentally do "10x + x", which I can actually add faster than my brain will return an answer from the post-10 part of the times table. (Not that I didn't memorize the 11s and 12s all the same at the time, but they got a lot less use and so a lot less reinforcement.)

> If you are building things in the US/UK/Canada then you are using feet and inches.

In the UK you are more likely to be using millimetres if working from any kind of design. Working in inches and feet would depend on your age and perhaps whether you are working on an older property that was designed in inches.

In the UK your designs and plans will be in mm, but your materials will vary between metric-rounding-of-imperial, (2400x1200mm) [1] imperial-but-labeled-in-metric (1220x2440mm) [2] and imperial-in-one-dimension-metric-in-the-other (38x144x2400mm) [3]. Wallpaper? 10m x 520mm for sure [4] but doors? 1981x762mm [5]. Cement? Back to metric, with 10kg and 25kg bags [6].

You'll also probably measure long distances in miles but short distances in meters; and weigh your ingredients in grams but your body in stone.

I guess what I'm saying is if you want a rationally designed measurement system, don't copy us Brits and especially don't copy our builders.

[1] http://www.wickes.co.uk/Knauf-Plasterboard-Square-Edge-2400x... [2] http://www.wickes.co.uk/Wickes-General-Purpose-OSB3-Board-18... [3] http://www.wickes.co.uk/Wickes-Studwork-%28CLS%29-38x144x240... [4] http://www.wickes.co.uk/Wickes-9006-Wallpaper-Embossed-White... [5] http://www.wickes.co.uk/Wickes-Skipton-Internal-Softwood-Doo... [6] http://www.wickes.co.uk/Blue-Circle-Extra-Rapid-Cement-25kg/...

You will almost certainly be working in millimetres, but because of ISO 2848, you will very likely be working in multiples of 300 millimetres:

https://en.wikipedia.org/wiki/Preferred_number#Buildings

Which is about a foot!

"If you are building things in the US/UK/Canada then you are using feet and inches."

I don't think that's been the case for a pretty long time in the UK - certainly DIY supplies are metric e.g. here is the Homebase site:

http://www.homebase.co.uk/en/homebaseuk/diy/timber/planed-ti...

I remember that memorizing the 11 column was trivial and fun, up to times 10 anyway.

That is only yet another reason in literally infinite ones why the US needs to actually push metric units. We bleed our stupidity into the UK and Canada while the rest of the world makes sense.

Makes sense..until you talk about time. Time makes no sense.

If you want to terrify an american, ask them about switching to metric time. https://en.wikipedia.org/wiki/Metric_time

This comes up all the time for me as americans use a different date format. I've had contract negotiations grind to a halt because someone was doing math based on 06/05/15 rather than 05/06/15.

Use something like 12/24/48 (US) or 48/12/24 (UK) if you want to "force" compliance, then you'll at least have an easy sanity check for each field.

The other benefit is you can check Y2038 compliance at the same time, but you should at least specify 4-digit years for whatever you're spec'ing, so you don't create the next Y2K.

I write everything either ISO or spelled out. Your dates would be 2015-06-05 or "June 6, 2015". It's an easy quick that everyone seems to be comfortable with.

Switch to ISO format. There's less confusion in 2015-05-06. Although the one time I tried to push for it, at a company with plants in both the US and Ireland, I couldn't quite get agreement and we settled on 2015-MAY-06.

No, the US is not exporting its stupidity to the UK in this case. There's a reason those units are called "imperial."

The US doesn't use Imperial units though! They use the US customary system (if that's quite the right term): https://en.wikipedia.org/wiki/United_States_customary_units

Though either way, you are quite right that the US has little influence on the UK in this respect.

> another reason in literally infinite ones

There are perhaps about three good reasons to push metric units, and the vast majority of us don't find them compelling enough to care. It's truly a non-issue.

As soon as I read your comment I thought about the Mars Climate Orbiter.

https://en.wikipedia.org/wiki/Mars_Climate_Orbiter

> in the US/UK/Canada

And the other 94% of the world population…?

So they don't have to learn it. Not sure what the problem is.

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