excel rolling 6 month calculation
<p>I have a row with 12 columns, one for each month, and each column has scores for each item I am tracking. </p>

<p>What I am trying to do is to get a rolling sum of the 3 last months and 6 months, but the problem is that the formula seems to retract 6 columns even if only data for Jan is on file.</p>

<p>This is a problem since in the columns before the monthly data I have various numbers that now get absorbed into the sum calculation.</p>

<p>Picture below for your reference. Thanks.</p>

<p><a href="http://i.stack.imgur.com/o5hKv.png" rel="nofollow">error</a> </p>