for example, 100 plus 105 equals 205
minus 106 oops i meant to put in 105, hit CE, hit the minus sign again, and the display reverts to 205 and i can put in the correct number
or, if you don't 'need' to see the display go back to the original number (205), then hit the CE and just type in the correct number. it will remember that you were subtracting