# Calculate difference from previous non-blank cell

I need a formula to calculate the difference in cells from the previous non-blank cell.  The data is formatted with dates in column A, readings (both blank and non-blank) in column B, and the difference from the previous reading in Column C.  See attached for an example.

``````Date            Reading	Diff
1/1/2010	54.4	0.0
1/2/2010	54.4	0.0
1/3/2010	54.4	0.0
1/4/2010	54.4	0.0
1/5/2010
1/6/2010
1/7/2010	54.4	0.0
1/8/2010	55.5	1.1
1/9/2010	55.5	0.0
1/10/2010	55.5	0.0
1/11/2010	56.5	1.0
1/12/2010
1/13/2010
1/14/2010	56.7	0.0
1/15/2010	56.7	0.0
1/16/2010	56.7	0.0
1/17/2010	56.9	0.2
1/18/2010	56.9	0.0
1/19/2010
1/20/2010	56.9	0.0
1/21/2010	56.9	0.0
1/22/2010	56.9	0.0
1/23/2010	56.9	0.0
``````
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Commented:
I take it that the output shown in column C isn't what you want, do you want C15 to be 0.2? If so try like this:
In C2 just put a zero then in C3 this formula copied down
=IF(B3="","",B3-LOOKUP(9.9E+307,B\$2:B2))
regards, barry
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VBA DeveloperCommented:
Put this in C3 and drag down:

=IF(ISERROR(B3-B2),"",B3-B2)

There's no difference for C2, since it's the start, so just set that to 0

Book1.xls
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VBA DeveloperCommented:
To make the formula more complete, try this:

=IF(B3="","",IF(B2="",0,IF(ISERROR(B3-B2),"",B3-B2)))

Book1.xls
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Author Commented:
Thanks to both you!!  Ended up using barryhoudini's.
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