Excel pivot table index option

osoto10 

It can be understood in simple unitary terms. Referring to the example in the article link shared by Riny_van_Eekelen , I've tried to distil the interpretation,

Index = Numerator / Denominator

Numerator = Value of cell / Grand Row Total

Denominator = Grand Column Total / Grand total of Grand Totals

or,

Numerator = Bottles sales in America / Bottles Sales across Regions
Denominator = America's sales / Global sales

or,

Numerator = Normalisation of Bottles sales across regions
Denominator = Normalisation of region sale across Globe

(Normalisation just changes figures to the scale of 1 in both Num. and Denom.)
or,
Numerator = "How much contributing" is the "American" "bottle" sales in "overall bottle" sales
Denominator = "How much contributing" is the "American" sales in "overall global" sales

So the fraction,
Index[american bottle] = Numerator / Denominator, at global scale,

1) Increases if "American" "bottle" sales increase
2) Decreases if "American" "bottle" sales decrease
3) Decreases if "American" "overall" sales increases as compared to other regions
4) Increases if "American" "overall" sales decreases as compared to other regions

1) and 2) are direct to understand that as the "American" "bottle" sales change (increase or decrease), so does the Index, so index in a way tells about the "influence" of american bottle in overall sales.

3) and 4) take into account how contributing is the region ("America") itself the to global sales. If America itself has a smaller %age contribution to global sales, then american bottle index (="influence") is bigger because same change in the absolute value of bottle sales in america would lead to bigger change in its %age contribution to overall sales as compared same change in the absolute value of bottle sales in some other region like Europe which was already contributing hugely to global sales. Thus the american bottle price change is more "sensitive" than European bottle price change.