Number representation in novels

Question

When writing out numbers, I've seen novels especially writing in weird formats. For example:

• 19- 一九
• 10- 一〇

I am assuming pronunciation wise, it is really じゅうきゅう and じゅう respectively. What's the motivation in using such a format rather than 十九 or 十. Is this the preferred way of writing when it comes to novels?

Answer 1

Yes this is one of the common ways to write numbers in vertical writing. 一九 and 十九 are both common, but the former style is usually preferred in the following situations:

1. When you write a code number, zip number, telephone number, room number, etc. (Imagine when you read 19 as "one nine" rather than "nineteen".)
2. When the number is larger than 100 (三千五百二十七 is harder to read than 三五二七)
3. In mathematical or statistical contexts
4. When you write many numbers in a page (in a list of dates, cooking recipe, etc.)

See this answer and this question for details.