View Full Version : Chart Question

10-19-2005, 05:52 AM
I've attached a file with a few graphs. This question can go with any of these graphs. They are all scatter plots, BTW.

How do I obtain values that are between two data points?

i.e. In the "Regular Polarity" chart, what is the current [i (A)] when the voltage is 3.35?? Or at any voltage, really???

I don't feel like performing hand calculations to do this, and I hope excel has a method for this : pray2:

TIA :thumb

10-20-2005, 11:54 AM
If you are willing to get close estimates of the values, then you might try reducing the major tick marks on the scale to something like 0.005 or 0.002 Use a visible grid. Then you can probably eyeball the approximate value you are looking for. Enlarging (zooming) the display would probably help. You're lucky that the graph is nearly linear.

10-20-2005, 09:32 PM
Excel does have some basic regression functions. You might be interested in the TREND() and LINEST() functions which you could apply to the linear portions of your chart. There is also a regression analysis tool in the Analysis Toolpack that I have never used.

There is also an 'Add Trendline' command in one of the menus when you have a chart data series selected. This can put the fit equation in a textbox for you, but the major problem with this method is that it fits the entire data series.

10-23-2005, 06:48 AM
You might also query Google and Google Groups for interpolation routines, if you want the value along a line segment connecting two adjacent points. There are quite a few different routines that have been posted over the years.