Down, right, down

So as well all know, the default writing direction for Japanese is vertical, from top to bottom. It's not unusual though for a column of text to contain a couple of characters aligned horizontally (left to right) — most commonly figures in Hindu-Arabic numerals, like a year or temperature. The other day though I noticed a case of double nesting:

積雪が [20 [cm]] を超えないうちに必ず雪おろしをして下さい。

"Clear the snow off [the roof of this bike shelter] before it piles up in excess of 20 cm thick."

The basic orientation is vertical. "20 cm" is a horizontal block within this, but the "cm" is a vertical block within that. Using red for vertical text and green for horizontal, this can be represented schematically as follows:

積雪が [20 [ cm ] ] を超えないうちに必ず雪おろしをして下さい。

Note that this is different from the standard fits-within-a-single-space "character" for centimeters, ㌢, which is just a case of warigaki (dividing part of a line into two smaller lines, both of the same orientation as the original line, to be read one after the other before proceeding to read the rest of the original line; there are a few examples on this page).

Popularity factor: 0

Aime la vérité, mais pardonne à l'erreur

LU d'R
Mail d'E

All fields optional. E-mail address will never be displayed, resold, etc. -- it's just a quick way to give me your e-mail address along with your comment, if you should feel the need. URL will be published, though, so don't enter it if it's a secret. You can use <a href>, but most other tags will be filtered out. (I'll fix it in post-production for you if it seems necessary.)