diff --git a/lib/launchpad/index.rb b/lib/launchpad/index.rb
index d682017..ce4fba4 100644
--- a/lib/launchpad/index.rb
+++ b/lib/launchpad/index.rb
@@ -6,6 +6,7 @@ module Launchpad
   # Provides a diff between local and remote file data by maintaining a cache
   # with pathnames and md5 hex digests.
   class Index
+    # @param [Launchpad::Patcher] patcher
     def initialize(patcher)
       @patcher = patcher
       @target_dir = Pathname.new Settings.read :install
diff --git a/lib/launchpad/patcher.rb b/lib/launchpad/patcher.rb
index c46f316..cb4ec66 100644
--- a/lib/launchpad/patcher.rb
+++ b/lib/launchpad/patcher.rb
@@ -14,14 +14,14 @@ def in_sync?
       index.diff.empty?
     end
 
-    # Determines the code to be executed when progress changes for the current
-    # operation.
+    # @param [Proc] block sets the callback to be run when progress is updated.
+    # @return [self]
     def on_update(&block)
       @update_callback = block
+      self
     end
 
-    # @return [Float]
-    #   denotes the completion percentage for the current operation.
+    # @return [Float] the completion percentage for the current operation.
     def progress
       @progress || 0.0
     end