anchor.diff:    <tbody>
     <% @irradiances.each do |irradiance| %>
       <tr>
  -        <td><%= irradiance.direct %></td>
  -        <td><%= irradiance.diffuse %></td>
  -        <td><%= irradiance.postcode_id %></td>
  -        <td><%= link_to 'Show', irradiance %></td>
  +      <td><%= irradiance.postcode.pcode %></td>
  +      <td><%= link_to 'Show', irradiance %></td>
         <td><%= link_to 'Edit', edit_irradiance_path(irradiance) %></td>
         <td><%= link_to 'Delete', irradiance, confirm: "Are you sure?", method: :delete %></td>
       </tr>
  
positive.code:   <colgroup>
      <col />
      <col />
    </colgroup>
    <thead>
      <tr>
          <th>Direct</th>
          <th>Diffuse</th>
          <th>Postcode</th>
          <th></th>
        <th></th>
        <th></th>
      </tr>
  
negative.code: 
  <br />
  
  <%= link_to 'Add irradiance', new_irradiance_path %>
  