HowCalc is the only calculator on the App Store that shows whats happening behind a calculation. It is a tool for learning and understanding in a world of instant answers.
Back in the day it was easy for a school teacher to ban the use of calculators but now that is barely possible. If a student cannot go without using a calculator it is better that they at least use one that shows them the answer and HOW that answer was calculated.
You cannot learn math without understanding it.