I like the calculator with its built-in function to issue a note with the functions and numbers typed in. In this way it is easy to review and verify the calculation done. The calculator can be used in both modes (vertical and landscape) with lots of buttons big enough to find the right ones with my stubby fingers. I have not checked its mathematical engine yet but I trust that this will be working. Definitively to recommend. why only 4 stars. For me 4 stars is already very good. I do not have much experience with this app so I might give it one more later. Ueli ----------