### Author Topic: How to use 3 axis graph  (Read 845 times)

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#### soldar

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##### How to use 3 axis graph
« on: June 23, 2024, 10:32:50 pm »
I have no idea how to read or use this type of graph.

Suppose I have a mixture 50% methane, 30% nitrogen, 20% oxygen. How do I find the corresponding point in the graph?
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#### Andy Chee

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##### Re: How to use 3 axis graph
« Reply #1 on: June 24, 2024, 01:25:47 am »
I have marked your coordinates below:

#### tooki

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##### Re: How to use 3 axis graph
« Reply #2 on: June 24, 2024, 01:36:17 am »
I’ve never used this type of graph before either, but based on the 12% oxygen as a clue, I suspect this is how it’s read. (And it seems to agree with Andy’s interpretation.)

#### soldar

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##### Re: How to use 3 axis graph
« Reply #3 on: June 24, 2024, 08:18:41 am »
I have marked your coordinates below:

OK, thanks, I think I understand. So there are two sets of lines leaving from each side but only one set applies to that side.

So I start with the percentage for methane and always follow the horizontal line, not the line that slopes downward. And I follow that line until I hit the nitrogen line which is only the ones sloping down and backwards and that necessarily will correspond to the Oxygen level which will be following the line which slopes down and forward.

So of the three sets of lines only one set applies to each "axis".

I think I got it. Thanks.
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#### ArdWar

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##### Re: How to use 3 axis graph
« Reply #4 on: June 24, 2024, 08:50:11 am »
With ternary plot like this the three axes are not independent of each other. x+y+z always add up to 1, so for a given value there are only one intersection that makes sense.
It should be obvious when you trace the wrong line. For example incorrectly following the 50% methane line downward until you meet the (also incorrect) 30% nitrogen line will leave you with either 70% or 50% oxygen.

To aid with interpretation, the chart's scale are usually not printed perpendicular like your example, but slanted to "continue" the correct lines (ex. oxygen scale should be rotated 30 degree CCW, nitrogen rotated 30 degree more CCW, methane 30 degree more CW).

Because of course there are people who draw the chart the other way around...

« Last Edit: June 24, 2024, 09:00:45 am by ArdWar »

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#### soldar

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##### Re: How to use 3 axis graph
« Reply #5 on: June 24, 2024, 09:08:15 am »
With ternary plot like this the three axes are not independent of each other. x+y+z always add up to 1, so for a given value there are only one intersection that makes sense.
It should be obvious when you trace the wrong line. For example incorrectly following the 50% methane line downward until you meet the (also incorrect) 30% nitrogen line will leave you with either 70% or 50% oxygen.

To aid with interpretation, the chart's scale are usually not printed perpendicular like your example, but slanted to "continue" the correct lines (ex. oxygen scale should be rotated 30 degree CCW, nitrogen rotated 30 degree more CCW, methane 30 degree more CW).

Yes, I realize all three have to add up to 100%

The graph you post is much more intuitive because it shows the lines of the three axis in different colors so you know what color line to follow.
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