My character dictionary is written in vertical style. In this dictionary, columns of text are sometimes divided into two smaller columns, which are read right-then-left. I've read that this is called 割注{わりちゅう}. It looks like this:
This says りんれつ.
Sometimes, when there's only a single character in each column, it looks like horizontal writing: right-to-left. Based on this experience, I figured any horizontal writing in the middle of vertical writing would be read right-to-left.
However, on the first page of the novel 魔術{まじゅつ}はささやく, I came across this:
I think it says 24. But that would be left-to-right! My intuition tells me it should be so, because they are not Chinese or Japanese characters. But is this really correct? My experience with my dictionary tells me it might say 42 instead. Which is it?
More generally, how do I tell which way to read horizontal writing in the middle of vertical writing?