Here is a comprehensive guide to understanding the various Indian nods:
Nod about the X-Axis:International Standard for Yes.
This means Yes in India as well.
Nod about the Z-Axis:
International Standard for No.
This means No in India as well ... most of the times.
This nod could also mean extreme appreciation.
eg: An Indian classical music enthusiast listening to an excellent live classical music performance.
The enthusiast can be found nodding a No and closing his eyes but with the look of orgasm on his face.
And the most popular - Nod about the Y-Axis:
What the nod means is very dependent on the position of the eyebrow
The meaning of the nod ranges from "barely okay" all the way to "oh! of course yes!"
Height Of Eyebrows vs Meaning of nod: