title: Rails subtract result for the previous result
body: <p>Thanks at all for previous answers in my questions<br>
  I have more one trouble to show my results i need to show the weight of my patients in view day after day<br>
  and i need to show more one column "weight losted" this is the weight of the day - weight of the previous day  but here is my code  </p>
  
  <pre><code>  p
  
  
  table
  thead
    tr
      th Date
      th Weight
      th IMC:
      th weight Losted:
  p
  strong pesos:
  tbody
    - @patient.weight.each do |m|
      tr
        td  = m.date
        td  = m.weight
        td  = (m.weight / (@patient.weight.first.inch**2).to_f).round(2)
        td  = m.weight - ?????????
  
  
  
  br  
  </code></pre>
  
  <p>I have no idea how to make this, because is to many results and i dont know how i call the last result to subract of the actual result<br>
  help me plz</p>