app/views/admin_mailer/school_group_meters_report.html.erb
<h1><%= @school_group.name %> meter report</h1>
<%= render 'shared/school_group_meter_report', email: true, all_meters: @all_meters %>
<h3>Loader Legend</h3>
<ul>
<li><span class="table-danger">No reading for 30 days</span></li>
<li><span class="table-warning">No reading for 5 days</span></li>
<li><span class="table-success">Recent reading</span></li>
</ul>