Reverse engineer lookup table from efficiency chart

I have this chart from a datasheet and I want to make a lookup table out of it to use in my calculations.
Using my ruler directly on the screen to make a table that is then converted really doesn't make me feel like a champ...
In the old Excel (2003) you could put this chart as a background and then make graphs and move the points around until they fit about right. However, even if I had that feature I have no good idea of how to make a lookup table from it.
Any ideas? I'm running Excel 2016 now.

Mussle chart.PNG

In the old Excel (2003) you could put this chart as a background and then make graphs and move the points around until they fit about right.

It seems like this option should still be available in 2016. I can still add the picture as a background image in 2007, and this (https://support.office.com/en-us/art...ustomshapefill ) suggests that you can still do it in 2016.

However, even if I had that feature I have no good idea of how to make a lookup table from it. Any ideas?

For a 2D lookup table, I would tend to structure the table something like

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I would then use an INDEX(table,MATCH(vertical x value lookup),MATCH(horizontal y value lookup))

Originally Posted by MrShorty

It seems like this option should still be available in 2016.

Missunderstanding. In Excel 2003 you could actually grab a datapoint in a chart and move it up and down and the corresponding cell would change value accordingly. Pretty neat.

I'm now researching picking coordinates from chart. It makes me go insane....

I'm now researching picking coordinates from chart. It makes me go insane....

I agree. When I have done this, I have preferred to simply hand enter the values in Excel, see the result on the chart, adjust if needed, and go on to the next point. It is tedious, but I usually feel like it is easier and faster than trying to coax VBA to read mouse position and translate that into something meaningful.

Ok. I'm reposting this problem in the VBA section:

https://www.excelforum.com/excel-pro...-in-chart.html

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You want to be able to enter x and y values and estimate the percentage values?

Yes, that is correct.

The workbook I posted was a start of a "lookup table generator". I would cut and paste a chart from somewhere as a background in an Excel chart.
The idea is to make that whole "get coordinates" -macro working and then expand it so that I can generate a lookup table automatically by clicking a number of points in the chart.

Here's a surface regression -- I don't know if it helps or not ...

Ha ha... That is hardcore! Thanks shg!

You're welcome.

Question; it seems like you purposely left out the last datapoints from all but one graph. Coincidence or regression strategy?
I would think more data points would be better and I would be more than happy to add them myself.
For the record, I have studied math/statistics up to about this level but my relationship with math is a love/hate one. Love the power it brings to engineering but hate the damages it inflicts on my brain when I try to learn it.

	C	D	E	F	G
3	1. Input Data
4	**Curve	88%	91%	92%	93%
5	x	y	y	y	y
6	0.01	60	110	180	276
7	200	65	115	190	292
8	400	70	135	230	368
9	600	90	180	325	504.0007
10	800	120	255	456.2508	700.0021
11	1000	160	348.0005	631.2521	956.0042

Left out the last data points?

These. Not that it is a problem, just curious.
Last points.PNG

I only digitized three points because that's sufficient for a parabola.

Having done that, I used the regression to tabulate all the values over the same interval, 0 to 1000. In retrospect, that was a mistake; I should have used the intervals for each curve, because the points outside that don't matter.

Here's a revised version with 25 coefficients that is a near-perfect fit (see the R2) within the extents of the curves. I used the regressed parabolas to generate the intermediate points.