diff --git a/Dockerfile b/Dockerfile
index 11f759d..e299a5c 100644
--- a/Dockerfile
+++ b/Dockerfile
@@ -1,6 +1,6 @@
 FROM ruby:2.7
 
-ENV BUILD_PACKAGES="apt-utils build-essential curl less nodejs sudo wget zsh libmariadb-dev libserialport-dev cron gr"
+ENV BUILD_PACKAGES="apt-utils build-essential curl less nodejs sudo wget zsh libmariadb-dev libserialport-dev cron"
 
 # throw errors if Gemfile has been modified since Gemfile.lock
 RUN \
diff --git a/Gemfile b/Gemfile
index c61cae7..fb5bd36 100644
--- a/Gemfile
+++ b/Gemfile
@@ -8,9 +8,6 @@ gem 'rufus-scheduler'
 gem 'daemons'
 gem 'mail'
 gem 'nokogiri'
-gem 'ruby-gr'
-gem 'gr-plot'
-gem 'histogram'
 gem 'numo-narray'
 gem 'i18n'
 gem 'gruff'
diff --git a/app/models/cost.rb b/app/models/cost.rb
index ae82895..74103ed 100644
--- a/app/models/cost.rb
+++ b/app/models/cost.rb
@@ -146,7 +146,7 @@ class Cost
     end
     g.labels = hours
     g.data :costs, costs
-    g.write("plots/easy_tariff_%s.png" % date.strftime("%F"))
+    g.write("plots/easy_cost_%s.png" % date.strftime("%F"))
     
     # return the sum cost
     costs.sum