When students start grade 9, they need to put aside the basic calculator they used in grade 8 - which is primarily just for adding, subtracting and dividing - and they need to get a more advanced scientific calculator with its sin/cos/tan buttons.
The scientific calculator that MathCubed recommends to grade 9 students has a 2-line screen display – Sharp, Casio, and Texas Instruments, among others, make calculators with a 2-line display.
The advantage of a two-line display is that what the student types into the calculator stays visible on the screen. What is great about this feature is it reduces careless errors since the student can see the math question they typed as well as the answer the calculator provides. For example, if the student types in 9 x 8, and then presses the equal button and gets the answer 72, 9 x 8 remains visible on the first line of the display and the answer, 72, is visible on the second line. If, however, the student has accidentally typed 9 x 9, they can see that error on the display (it hasn’t been replaced by the answer) and they can correct it. A slip-up error has been avoided!