Viewing previous equations
To view all the previous equations you have entered, go to the "Equations" tab. You can then scroll through the equations. If you tap on a equation, it will insert it into the equation box in the keypad view.
Editing previous equations
To edit an equation you have previously entered, go to the "Equations" tab, and tap on the equation you want to edit. This will insert it into the equation box in the "Keypad" tab. You can then tap the equation box to move the cursor around, or tap and hold to bring up the keyboard.
Manually editing the equation
To manually edit the equation, tap and hold the equation box. This will bring up the keyboard, and you can then enter an equation using that. When you are finished, tap the "Done" button, and then tap the "=" button to calculate the equation.