Very good!!!

Of course there are many scientific calculators on AppStore. However, the user interface of this one is very good: 1) the most used scientific functions are directly accessible (no 2nd key).
2) the calculation is edited on the first row of the display when the result is shown on the second one. The display can also be scroll to see and reuse the old calculations.
3) the user interface is very comfortable and clean.

A memory and a landscape mode would be useful.

Pascalito65 about Calculate: Advanced Calculator