ThriftyCalc has five easy to use calculators build for the sole purpose of people money.
Once you open the app it will take you through a short tutorial to help you start saving right from the get go.
Each calculator has it's own page and all you have to do is swipe between the calculators and never lose your place.
Calculate orange juice on one page and cans of beets on the next without ever losing your progress. Then when you are done, just shake the phone to clear the page.