One can always see on the news for example, the movement of stock indexes.
Say for example: S&P +5.15 (0.05%) or S&P -0.57 (0.001%)
But how would I calculate the 2 numbers above? (+5.15 and 0.05%)?
For example, I checked on google finance and found for the S&P 500
Oct 22, 2012
Oct 23, 2012
So for the change in the S&P 500 for October 23rd, do I take the difference between the closing prices of Oct 22nd and Oct 23rd? Or the difference between the opening and closing price of Oct 23rd?