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Now, I have an Excel file with measurements I made of some color patches (I work at a Press company), with a device called spectrophotometer.

Here it is: https://docs.google.com/open?id=0B0i8fdSf2ihzRlFYNWd4anItenM

Density and Hue are two characteristics of each color patch. The thing is: I'm looking at a non-linear increase between the 25 Color Density measurements I took, but I NEED to know exactly how the color's Hue changes as the color's Density increases.

For that, I needed Excel to give me round numbers for the X axis (for example 0,70 to 1,50 in 0,05 increments).

And for that, obviously, I needed Excel to calculate the probable Hue Values corresponding to those ghost/round/not-given values of Density (like a kind of advanced rule of three).

So, can anyone help me on that?

Thanks a lot!

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Please indicate the version of Excel you are using so that we can give better answers. Adding a tag is fine. –  Julian Knight Jul 5 '12 at 16:51
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2 Answers

If you do need values of hue for density values(0.70,0.75 and so on):

Just draw X-Y Scatter plot with smooth lines and markers.

If you do need the hue values for those density values:

You cannot get the exact value in excel.
Even if you could, you probably should not use that value as accurate prediction.

When excel draws that smooth graph for you, it basically fits a curve through your data points using some technique. There are many types of curves like bezier, cubic spline etc.

Now, each of this curve will look different and will give different value of hue for intermediate density values.

Bottomline is this is more of math job than excel. You should figure out which curve better the predicts the pattern that you are trying to map and fit that curve. Once you have curve equation, you can determine hue for any density value.

The point here is if you were to use some other graphing software that allows you to get hue for any density value, that still wont be accurate.

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Boys, you saved the day. Thank you very much. This is exactly what I needed. –  tcheregati Jul 17 '12 at 19:50
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It sounds like you want to use an X-Y Scatterplot.

Select all of the data, choose X-Y Scatterplot from the Insert menu, and from there, you can choose to plot only points, points and a straight line, points and a curved line, or any of these without showing individual points.

After you have the chart, right click on the X-axis and choose Format Axis. Here you can change the major units to fixed and set the increment, as well as setting the minimum and maximum.

Once you have the chart, if you right click on a data point, you can add a trendline (exponential, linear, logarithmic, polynomial, power) and display the equation for that trendline on the graph. Then you can use this equation for calculating values at the 0,05 increments, and you will also be able to see where these should lie by looking at the trendline in your graph.

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Boys, you saved the day. Thank you very much. This is exactly what I needed. –  tcheregati Jul 17 '12 at 19:50
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