I'm curious about this issue because although I've purchased double convex Yunzi stones size 33 (beautiful)...I was puzzled why there are size 41 stones. Is there a specific reason for a different sized Yunzi stones? And what size Yunzi stones do the pros play with over the board if the assumption is they play using a normal sized 19x19 board?

Usually, the "size" refers to the thickness, not the diameter, of the stones.
Of course, different people have different preferences,
but I heard Cho Chikun's favorite for shell stones was size 38 (10.7 mm),
and although I didn't understand it at first, after a few years, I came to the same conclusion as Mr. Cho.

(That said, some pros, especially those in China, have only very basic sets for their personal use.
Some pros don't even have any sets at home! They work at a Go school, and when they go home,
they don't want to work any more. )

For national and international tourneys, the equipment used depends on each individual event,
the organizer, the sponsor, the venue, etc.

Now that I know the conversion factor, I wonder what the unit of the "size" is

karaklis, I don't quite understand your question, but maybe you'll find this helpful?
http://www.kurokigoishi.co.jp/english/o ... index.html

I guess you mean size 38 ?? = 10.7 mm where the answer is what is ??. From EdLee's link you can see though that for the larger sizes the difference is 1 "??" = 0.3 mm but for smaller it's less so for size 30 to 28 = a difference of 0.5 mm. Weights and measures isn't my thing really but my guess (and I'm usually wrong) is that since it doesn't appear to be a linear relationship that it's simply an industry standard convention?

However, wikipedia (retreat of the ignorant) says 0.3 mm is a rin.

http://en.wikipedia.org/wiki/Japanese_units_of_measurement

_________________
I am John. John-I-Am.

For reference I purchased my Yunzi double convex stones from YMI. They're being listed as 9.2mm (size 33) Does this help matters?

Hi, again it's just guess work but as I understood it karaklis wanted to know whether "stone size 38" the 38 has units (e.g. meters etc) not what the stone sizes correspond to in mm. It seems that they nearly do - that size differences between them correspond to single "rin" for the larger stones but its some industry standard measure and the difference of 1 rin between sizes doesn't hold for the smaller ones.

unless I've made a mistake in my plot (using the kurokigoishi values), this is what I mean:



The red line is the Size/Thickness relationship if you assume Thickness = (Size*0.3 - 0.7) with the *0.3 term needed to convert from rin to mm.

_________________
I am John. John-I-Am.

Indeed, the question was about the name of the unit, e.g. size = 33 units of what? E.g. centi-inch (would almost match: one unit of "size" would be around 1.1 centi-inch) but not exactly, also the "rin" doesn't seem to match exactly (one unit of "size" would be around 0.9 rin). So I wonder what the name of that unit is..

I'm basically as in the dark as people in this thread on the terminology because YMI is describing the Yunzi stones I've purchased as being 9.2 mm (size 33). Don't ask me how they make that determination. The only reason why this getting me curious is the option to buy Yunzi stones far more expensive...the (size 41) that is...and I was curious to know what the pros use...especially those televised Go contests we see on Korean Baduk TV, etc.

For example do Go organizations have an official designation of Go stone size for OTB play?

Is that a correct or meaningful question?
Take shoes, for example, "U.S. men's shoes, size 8.5", "E.U. men's shoes, size 41" --
the sizes do not have any units (do they?),
but they do correspond to some physical lengths.

Same thing with "Size Small", "Size Medium", or "Size Large" at McDonald's or Starbucks -- there is no unit,
but they correspond to some volumes, correct?

Again, see this chat: http://www.kurokigoishi.co.jp/english/o ... index.html
I believe it is not size 38 of anything; only that "Size 38" means "within some range of 10.7mm thickness".

Hmm, if you look at the measuring device in a shoe store I think you'll see that they are equally spaced. Maybe the sizes on clothes would be a better example? (for women, at least, the sizes start as zero, so it's clearly an ordinal relationship rather than a measure relationship.)

In Korea,

Korean Baduk league use 35 size stone
Matches open in Korean Kiwon(Ki-in) use 35 size stone

In competitions opened elsewhere, pros will use stones the sponsor provides