Complications with equal weighted index.

So , price weighted index is a bit more intuitive , because it matches the returns on a portfolio , that has bought the same number of shares of each stock in it.
Ex : Stock A – $3 , Stock B – $7 , Stock C-$8 , Price W. Index = (3+7+8)/3 = 6. one can clearly see that that it seems as if we have bought 1 share of each stock , while calculating PWI.

Equal weighted index confuses me because it seems to more like an “index return” than an index, ((calculated as the “arithmetic average return” of the stocks)). An index return is the percentage change in the index value(could be calculated using price index or return index).

Also the fact that it mimics a portfolio , with equal $ amount invested in each stock , is not that intuitive.

Do we calculate an Equal Weighted index like this ?

Stock A – $3 , Stock B – $7 , Stock C-$8 , for the 1st period , in the second period the price of the stocks change to Stock A – $4 , Stock B – $5 , Stock C-$10.
EWI = (return on A + return on B + return on C) / 3 (unlike the Price Weighted Index , I can’t really imagine How I have invested equal dollar amount in each stock )

return on A = 33.33%
return on B = -25.57%
return on C = 25.00%
EWI = ((.3333+(-.2557)+.2500)/3)*100=10.92

Also it says that the matching portfolio would have to adjusted periodically as prices change so that the “value of all security positions are made equal each period”. This doesn’t makes sense to me either.What are the adjustments and why are they needed?