Comment by travisjungroth | Hacker News Reader

Comment by travisjungroth | Hacker News Reader

I enjoy dozenal. I also enjoy weightlifting. An interesting property of dozenal is how compatible it is with American barbell weights. I haven't heard anyone mention this before (who knows why. the intersection of mathematicians and powerlifters?)

American weights are normally a 45lb barbell, 45lb plates, and then additional smaller plates. The large plates are just called "plates" and counted on one side. 1 plate -> 135 (45*2+45bar), 2 plates -> 225, 3 plates -> 315, 4 plates -> 405. These seemingly weird numbers become "round" when you've been lifting them a while.

What about jumps smaller than that? It gets a little weird. 45 doesn't exactly break up nicely. You might have 35s, definitely 25s, maybe 15s (especially olympic lifters) then 10s, 5s, and 2.5s (called "twos"). "A plate, a twenty-five and a two" is 190. Then you get into "washers". Maybe a 1.25. Or if you have a few pairs of 0.75s and 0.5s you can make any integer.

This is not ideal. You need to have more different types of plates than is most necessary. The math is summing up lots of odd numbers.

Enter dozenal plates. I'll put a d at the front for dozenal measurements. A dozenal plate would be d40, or 48lbs. Pretty darn close to the 45s. The bar is also d40. So a bar with a plate on each side is... d100. Well that's nice. 2 plates -> d180, 3 plates -> d240, 4 plates -> d300. And the smaller plates: d20, d10, d6, d3. If those jumps of 6 total pounds are too big, you could add d1.6, and d0.9 washers. All perfectly split.

That's a neat trick. Of course some of the number weirdness comes from that fact that standard kg plates are translated approximately into lbs in the US. So your 45lb plate is actually a 20kg plate and your 25lb plate is based on a 10kg plate. Although 10kg is actually around 22lb. I'm not sure whether the same colour plates genuinely weigh slightly differently in the US vs the rest of the world.

They do weigh at their marked weight (nowadays at least). But you’re right they’re just slightly modified kg plates.

Not much of a powerlifter, but my working squat was > 2x bodyweight for a while.

I find it easier to lift weights in metric. It helps that I'm EU based, so my plates are in KG.

One plate is 20kg, and the bar is also 20kg Jumps smaller than that, 10kg, 5kg, 2.5kg, 1.25 kg. I've never needed to get down to washers, 1.25 kg jump is small enough to make even with 'small muscle' exercises (wrist curls)

Powers of two all the way down, sums are easy.

The trick is to do sets of 12. Sets of 10 are too easy. So the dozenal still comes in :)

I find lifting in metric way easier. I can do about twice as much!

I don't understand the benefit - either system can accurately represent any integer number of pounds, right? And as you said, after a while the "weird" numbers become normalized after a little while. And it seems like you need the same number of different smaller-weight plates either way (45/25/10/5/2.5) vs d(40/20/10/6/3). If you want the plates to be integer multiples of each other, why not go with the already-widely-adopted kilogram weights?

Also, with d(6/3/1.6/0.9), you're still summing up odd numbers.

If you do the math all the time it’s easy, but most don’t.

You have one more plate in dozenal before you have to get fractional. And 6 and 3 aren’t weird numbers in dozenal. They’re like a half and quarter, respectively. 6+6=10.

Ah, that makes some sense, thanks.

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