diff --git a/app/controllers/quantities_controller.rb b/app/controllers/quantities_controller.rb
index 1136c76..4889123 100644
--- a/app/controllers/quantities_controller.rb
+++ b/app/controllers/quantities_controller.rb
@@ -1,6 +1,6 @@
 class QuantitiesController < ApplicationController
   before_action :find_project_by_project_id, only: [:index, :create]
-  before_action :find_quantity, only: [:destroy]
+  before_action :find_quantity, only: [:destroy, :toggle]
   before_action :authorize
 
   def index
@@ -26,6 +26,11 @@ class QuantitiesController < ApplicationController
     redirect_to project_quantities_url(@project)
   end
 
+  def toggle
+    @quantity.update(primary: !@quantity.primary)
+    redirect_to project_quantities_url(@project)
+  end
+
   private
 
   def quantity_params
diff --git a/app/views/quantities/index.html.erb b/app/views/quantities/index.html.erb
index f9f8d37..bcd54a4 100644
--- a/app/views/quantities/index.html.erb
+++ b/app/views/quantities/index.html.erb
@@ -45,7 +45,11 @@
             <td class="name"><span><%= q.name %></span></td>
             <td class="domain"><%= q.domain %></td>
             <td class="description"><%= q.description %></td>
-            <td class="action"><%= delete_link quantity_path(q), data: {} %></td>
+            <td class="action">
+              <%= link_to l(:button_toggle), toggle_quantity_path(q),
+                {method: :post, class: "icon #{q.primary ? "icon-fav" : "icon-fav-off"}"} %>
+              <%= delete_link quantity_path(q), data: {} %>
+            </td>
           </tr>
         <% end %>
     </tbody>
diff --git a/config/locales/en.yml b/config/locales/en.yml
index 17eb5eb..585f381 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -10,6 +10,7 @@ en:
   field_domain: 'Domain'
   field_parent_quantity: 'Parent'
   field_shortname: 'Short name'
+  button_toggle: 'Toggle'
   activerecord:
     errors:
       models:
diff --git a/config/routes.rb b/config/routes.rb
index 076193d..bfdc24c 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -11,7 +11,9 @@ resources :projects do
       get 'nutrients', on: :collection
     end
     resources :sources, :only => [:index, :create, :destroy]
-    resources :quantities, :only => [:index, :create, :destroy]
+    resources :quantities, :only => [:index, :create, :destroy] do
+      post 'toggle', on: :member
+    end
     resources :units, :only => [:index, :create, :destroy]
   end
 end
diff --git a/init.rb b/init.rb
index ea7f4e8..6f87ae9 100644
--- a/init.rb
+++ b/init.rb
@@ -24,7 +24,7 @@ Redmine::Plugin.register :body_tracking do
       :body_trackers => [:defaults],
       :ingredients => [:create, :destroy, :import],
       :sources => [:create, :destroy],
-      :quantities => [:create, :destroy],
+      :quantities => [:create, :destroy, :toggle],
       :units => [:create, :destroy],
     }, require: :loggedin
   end