Plot one point on a graph based on 3 variables

[darko1515s]

Hello all

I am wondering how can I plot a single point on a graph based on 3 variables.
I have bellow example:
All numbers are in precent: 40% Argila (Clay) , 30% Praf (Dust), 30% Nisip (Dust) and based on those numbers point "A" is plotted on the graph.
No matter the precent of those 3 variables how to show point "A" on my graph?

 

[Kaper]

Step by step instruction could be found here: How to plot a ternary diagram in Excel or as a video: