Thanks for a great plugin. Unfortunately, many of the sites I admin use SSL/HTTPS for their WordPress admin area and the URL for the Google Chart displayed by this plugin doesn't account for that. This oversight leads to partially secure browser messages when viewing the WP Dashboard.
I've tweaked the function
create_google_chart_url() starting on line 183 in
gad-data-model.php to accommodate secure WordPress installs. Here's a pastebin with the updated code for that function: http://pastebin.com/hWCmQSKc
Maybe you could incorporate this change into the plugin's source? Otherwise, at least this will help me and anyone else looking to tweak the plugin with witha good bookmark.