Where a blank cell is found in column B, sum the previous two cells in column B.

[huberttheg]

Can someone assist me with this:
Where a blank cell is found in column B, sum the previous two cells in column B. Continue until no data remains. I've included a sample:

COLUMN A COLUMN B
<TABLE style="WIDTH: 252pt; BORDER-COLLAPSE: collapse" border=0 cellSpacing=0 cellPadding=0 width=335><COLGROUP><COL style="WIDTH: 172pt; mso-width-source: userset; mso-width-alt: 8374" width=229><COL style="WIDTH: 80pt; mso-width-source: userset; mso-width-alt: 3876" width=106><TBODY><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; WIDTH: 172pt; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20 width=229>7/1/2008 12:00:00 AM - 12:30:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; WIDTH: 80pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" width=106 align=right>0</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 12:30:00 AM - 1:00:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>0</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20></TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" class=xl63></TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 1:00:00 AM - 1:30:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>0</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 1:30:00 AM - 2:00:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>1</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20></TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8"></TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 2:00:00 AM - 2:30:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>0</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 2:30:00 AM - 3:00:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>1</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20></TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8"></TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 3:00:00 AM - 3:30:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>0</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 3:30:00 AM - 4:00:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>0</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20></TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8"></TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 4:00:00 AM - 4:30:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>0</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 4:30:00 AM - 5:00:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>0</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20></TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8"></TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 5:00:00 AM - 5:30:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>0</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 5:30:00 AM - 6:00:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>0</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20></TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8"></TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 6:00:00 AM - 6:30:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>8</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 6:30:00 AM - 7:00:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>5</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20></TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8"></TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 7:00:00 AM - 7:30:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>15</TD></TR><TR style="HEIGHT: 15pt" height=20><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; HEIGHT: 15pt; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" height=20>7/1/2008 7:30:00 AM - 8:00:00 AM</TD><TD style="BORDER-BOTTOM: #d4d0c8; BORDER-LEFT: #d4d0c8; BACKGROUND-COLOR: transparent; BORDER-TOP: #d4d0c8; BORDER-RIGHT: #d4d0c8" align=right>6</TD></TR></TBODY></TABLE>

 

[Peter_SSs]

huberttheg

You requirement is not perfectly clear to me. See if one of these methods is any use.

Method A
In cell C3 use =IF(B3="",B1+B2,"") and copy this formula down.

Method B
Select column B by clicking its heading label.
Edit|Go To...|Special|Blanks
Enter the following keystroke sequence
= uparrow + uparrow uparrow Ctrl+Enter
You would then need to go to the end of your data and enter the final formula separately.

If neither of those gets you what you want, please give some more detail.