Assuming your table is in A1:B6 and D1 has the fuel capacity you want to look
up

=IF(ISNA(MATCH(D1,A1:A6,0)),TREND(OFFSET(B1,MATCH( D1,A1:A6)-1,0,2,1),OFFSET(A1,MATCH(D1,A1:A6)-1,0,2,1),D1),VLOOKUP(D1,A1:B6,2,FALSE))

Change ranges to suit and test it out. The assumption I got from your
example is the data is linear between each point. Does it give the results
you want?


"asevie" wrote:


Fairly simple problem as far as logic is concerned, but I've never tried
to replicate this type of forumula in Excel. Perhaps some advice...

I'm duplicating a weight and balance slide rule used for aircraft
center of gravity calculations. In this particular aircraft, as fuel is
burned, the center of gravity changes exponentially. For example,
between 0 and 5000 pounds of fuel burn has a linear change on the
index, for each 1000 pounds there is a change of approximately 0.17 on
the index scale, between 5000 and 10000, the number goes to 0.2, etc.
I've got all of these plotted in a simple 2 column spreadsheet. What I
would like to do is fill in the total fuel capacity, say 7800 pounds,
and have the spreadsheet look to the 2 closest values and extrapolate
the number. So, for the above example 7800, the function or formula
would look to my nearest values, -2.4 for 7000 and -2.6 for 8000, and
arrive at the the correct -2.56.

Any ideas on how to accomplish this? Thank you.


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asevie
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