diff --git a/app/controllers/units_controller.rb b/app/controllers/units_controller.rb
index 064726c..bae6949 100644
--- a/app/controllers/units_controller.rb
+++ b/app/controllers/units_controller.rb
@@ -1,19 +1,19 @@
 class UnitsController < ApplicationController
+  before_action only: [:new] do
+    find_unit if params[:id].present?
+  end
   before_action :find_unit, only: [:edit, :update, :destroy]
 
   before_action except: :index do
     raise AccessForbidden unless current_user.at_least(:active)
   end
-  before_action only: [:edit, :update, :destroy] do
-    raise ParameterInvalid unless current_user == @unit.user
-  end
 
   def index
     @units = current_user.units
   end
 
   def new
-    @unit = current_user.units.new
+    @unit = current_user.units.new(base: @unit)
   end
 
   def create
@@ -52,6 +52,6 @@ class UnitsController < ApplicationController
   end
 
   def find_unit
-    @unit = Unit.find(params[:id])
+    @unit = Unit.find_by!(id: params[:id], user: current_user)
   end
 end
diff --git a/app/views/units/_form.html.erb b/app/views/units/_form.html.erb
index b1c22ce..3f268dd 100644
--- a/app/views/units/_form.html.erb
+++ b/app/views/units/_form.html.erb
@@ -1,6 +1,6 @@
 <%= fields_for @unit do |form| %>
   <tr id="<%= dom_id(@unit) %>" onkeydown="processKey(event)">
-    <td>
+    <td class="<%= class_names({subunit: @unit.base}) %>">
       <%= form.text_field :symbol, form: :unit_form, required: true, autofocus: true, size: 12,
         maxlength: @unit.class.columns_hash['symbol'].limit, autocomplete: "off" %>
     </td>
@@ -10,8 +10,9 @@
     </td>
     <td>
       <% unless @unit.base.nil? %>
-        <%= form.number_field :multiplier, form: :unit_form, step: "any", size: 10,
-          autocomplete: "off" %>
+        <%= form.hidden_field :base_id, form: :unit_form %>
+        <%= form.number_field :multiplier, form: :unit_form, required: true, step: "any",
+          size: 10, autocomplete: "off" %>
       <% end %>
     </td>
 
@@ -23,4 +24,3 @@
   </tr>
   <!-- TODO: display error_messages_for unit -->
 <% end %>
-
diff --git a/app/views/units/_unit.html.erb b/app/views/units/_unit.html.erb
index e4e2b77..88fab3e 100644
--- a/app/views/units/_unit.html.erb
+++ b/app/views/units/_unit.html.erb
@@ -1,11 +1,17 @@
-<tr>
-  <td class="link">
-    <%= link_to unit.symbol, edit_unit_path(unit), class: unit.base.nil? ? '' : 'subunit' %>
+<tr id="<%= dom_id(unit) %>">
+  <td class="<%= class_names('link', {subunit: unit.base}) %>">
+    <%= link_to unit.symbol, edit_unit_path(unit) %>
   </td>
   <td><%= unit.name %></td>
   <td class="number"><%= scientifize(unit.multiplier) if unit.multiplier %></td>
+
   <% if current_user.at_least(:active) %>
     <td class="actions">
+      <% if unit.base.nil? %>
+        <%= image_link_to t(".add_subunit"), "plus-outline", new_unit_path(unit),
+          onclick: 'this.blur();', data: {turbo_stream: true} %>
+      <% end %>
+
       <%= image_button_to t(".delete_unit"), "delete-outline", unit_path(unit),
         method: :delete %>
     </td>
diff --git a/app/views/units/new.turbo_stream.erb b/app/views/units/new.turbo_stream.erb
index 6cbfd9b..6f347f4 100644
--- a/app/views/units/new.turbo_stream.erb
+++ b/app/views/units/new.turbo_stream.erb
@@ -1,5 +1,13 @@
-<%= turbo_stream.prepend :units do %>
-  <%= render partial: 'form' %>
+<%= turbo_stream.disable :add_unit %>
+<%= turbo_stream.disable_all 'td.actions .button' %>
+
+<% case %>
+<% when @unit.errors.present? %>
+  <%= turbo_stream.replace @unit, partial: 'form' %>
+<% when @unit.base.nil? %>
+  <%= turbo_stream.prepend :units, partial: 'form' %>
+<% else %>
+  <%= turbo_stream.after @unit.base, partial: 'form' %>
 <% end %>
 
 <%= turbo_stream.update :unit_form_frame do %>
diff --git a/config/locales/en.yml b/config/locales/en.yml
index f1d264a..c44f31e 100644
--- a/config/locales/en.yml
+++ b/config/locales/en.yml
@@ -34,6 +34,7 @@ en:
       users: Users
   units:
     unit:
+      add_subunit: Subunit
       delete_unit: Delete
     index:
       add_unit: Add unit
diff --git a/config/routes.rb b/config/routes.rb
index 2535626..0aa8f2d 100644
--- a/config/routes.rb
+++ b/config/routes.rb
@@ -2,7 +2,7 @@ Rails.application.routes.draw do
   devise_for :users, path: '', path_names: {registration: 'profile'},
     controllers: {registrations: :registrations}
 
-  resources :units, except: [:show]
+  resources :units, except: [:show], path_names: {new: '(/:id)/new'}
 
   resources :users, only: [:index, :show, :update] do
     member do