title: Understanding forecast accuracy MAPE, WMAPE,WAPE?
body: <p>I am new to the forecast space and I am trying to understand the different forecast accuracy measures. I am referring to the below link
  <a href="https://www.otexts.org/fpp/2/5" rel="nofollow noreferrer">https://www.otexts.org/fpp/2/5</a></p>
  
  <p>Can anyone please help me understand the below things:
  1. MAPE: I am trying to understand the disadvantage of MAPE "They also have the disadvantage that they put a heavier penalty on negative errors than on positive errors. " Can anyone please provide an example to explain this in detail?
  2. Also, I was assuming that WMAPE and WAPE are same. I saw this post at stackoverflow which formulates them differently. 
  <a href="https://stackoverflow.com/questions/12994929/whats-the-gaps-for-the-forecast-error-metrics-mape-and-wmape">What&#39;s the gaps for the forecast error metrics: MAPE and WMAPE?</a></p>
  
  <p>Also, can you please help me understand how the weights are calculated? My understanding is higher the value more important it is. But I am not sure how the value is calculated.
  Thanks in advance!</p>