Use ndash for numerical relations.

railties/guides/source/association_basics.textile

@@ -195,7 +195,7 @@ end
 
 h4. Choosing Between belongs_to and has_one
 
-If you want to set up a 1-1 relationship between two models, you'll need to add +belongs_to+ to one, and +has_one+ to the other. How do you know which is which?
+If you want to set up a 1–1 relationship between two models, you'll need to add +belongs_to+ to one, and +has_one+ to the other. How do you know which is which?
 
 The distinction is in where you place the foreign key (it goes on the table for the class declaring the +belongs_to+ association), but you should give some thought to the actual meaning of the data as well. The +has_one+ relationship says that one of something is yours - that is, that something points back to you. For example, it makes more sense to say that a supplier owns an account than that an account owns a supplier. This suggests that the correct relationships are like this: