diff --git a/book/source/04-certificates.md b/book/source/04-certificates.md
index abd5035..d647e12 100644
--- a/book/source/04-certificates.md
+++ b/book/source/04-certificates.md
@@ -126,7 +126,7 @@ OpenPGP certificates can contain multiple [User IDs](https://www.ietf.org/archiv
 :name: fig-user-ids
 :alt: Depicts a diagram with white background and the title "User IDs". Inside, a public primary component key for certification and a User ID is shown. A green arrow points from component key to User ID and is annotated with a signature.
 
-OpenPGP certificates can contain any number of User IDs
+Relationship of User ID to primary component key in an OpenPGP certificate
 ```
 
 A typical User ID identity is a UTF-8-encoded string composed of a name and an email address. By convention, User IDs align with the format described in [RFC2822](https://www.rfc-editor.org/rfc/rfc2822) as a *name-addr*.