How to get an Intermediate value ?

Dear Friends

Herewith I attached one excel file. In that file temperatures with respect to their density is plotted. My requirement is I want to get an intermediate value.

For example what is the value of Density when the temperature is 57°C. To do this Please anybody suggest an one word formula like TREND or FORECAST etc without drawing graph.

Thanks

thilag

AndyPS's solution can work, though the data don't look exactly linear with temperature.

When I do a problem like this, I like to see if there's a theoretical equation underlying the data that will do better. Looking at the spreadsheet, I infer that these are densities for air? If so, and it looks like they are densities at about 1 atm pressure, I would probably use a simple equation like the ideal gas law (n/V=n*MW/V=P/RT). Ideal gas appears to be in error by, at most, 0.2%.

For greater accuracy, I would probably reduce these data to compressibilities (z=PV/nRT), fit the compressibilities, then use the correlated compressibilities to get the density at other temperatures.

MrShorty's quite right about the need to look for the underlying physics in solving your problem more precisely. Excel's TREND and FORECAST functions are straight line fits to data and so are not too good with non-linear relationships. The way forward is to transform the data to a coordinate set that results in a (close to) linear relationship then apply the least squares fit.
It is always useful to look at the goodness of fit (e.g. PEARSON) to see if the relationship holds well - graphing is also useful.
A simple transform for the gas equation is to change the temperature from Celsius to Kelvin^-1 - i.e. divide 1 by C+273. This gives a very good fit. Assuming the new value is in cell A21, the following formulae work:

=FORECAST(1/(273+A21),$B$4:$B$18,1/(($A$4:$A$18)+273))
=TREND($B$4:$B$18,1/(($A$4:$A$18)+273),1/(273+A21))

The arguments are a little complex but they allow the coordinate transform without the need to calculate a new column.

Dear Mr. AndyPS

Sorry for my very late reply.

Thanks for your Immediate Help.

My Sincere thanks to you.


thilag