Can someone explain why in the screenshot the opening price is $245 and the closing price is $251 (a difference of $6+) but the green text shows the movement as only +$1.38?
The previous day, the stock closed at $250.22. While it opened lower in the morning, that drop was erased and the stock closed at $251.60, a gain of $1.38 over the previous day's close.
Stock changes are always quoted relative to the previous day's closing price, not the current day's opening price.
Consider the number given : 251.60
Check the Increment : +1.38
Undo that Increment , that is , calculate 251.60-1.38 to get 250.22
Look at the Data to figure out where the number 250.22 is given.
Aha , it is "Prev Close" !
We might even calculate "100 [1.38/250.22]" to get the Percentage Increment "0.55%" which is given against the Increment.
Hence , we see that all the numbers are against "Previous Close" !
This makes a lot of sense & is very useful :
[ 1 ] You can track the Daily Increments over some time interval of Interest , by just taking the Starting Point & adding all the Increments ( & Decrements ! ) to get Current Value.
Eg you bought it at 500.00 , on Monday & the Daily Increments were +1.00 , -2.10 , +0.10 , +3.00 , +3.00 : The Current Value at the End of Day 5 will be 500.00 + 1.00 + -2.10 + +0.10 + +3.00 + +3.00 = 505.00
We can not get this via Starting Value. It works with "Previous Close" Values.
[ 2 ] It is the Standard Base Value to calculate Daily Percentages.
[ 3 ] We have Continuity between Previous Close & Current Value which will make the long term Chart more Consistent.
[ 4 ] The Dividends , Average returns , Interest , ETC are calculated based on Closing Price.
[ 5 ] Even the Stock Market Index @ the time of closing is calculated with Closing Stock Price Values.
[ 6 ] There are other technical uses too.
Here are few random references about Closing Price & why/how it is used to calculate Increments & Percentages :