Often we work with large data sheets and it becomes tedious if you want to compare data / formulas etc. You can try split (menu > window > split or alt+w+s) to break the sheet in to two. But there is another cool thing you can do, open a new window for the spreadsheet. Just press Alt + w + n (menu > window > new window) to open the same spreadsheet in 2 windows. Any changes you make in one window are immediately visible in another window(s).
Bonus tip: you can do the same thing with WORD and POWER POINT as well, cool eh?