Apple iPhone 4G - Manual (Page 154)

Calculator
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Using the Calculator
Tap numbers and functions in Calculator just as you would with a standard calculator.
When you tap the add, subtract, multiply, or divide button, a white ring appears
around the button to let you know the operation to be carried out. Rotate iPhone to
get an expanded scientific calculator.
Standard Memory Functions
 C: Tap to clear the displayed number.
 MC: Tap to clear the memory.
 M+: Tap to add the displayed number to the number in memory. If no number is in
memory, tap to store the displayed number in memory.
 M–: Tap to subtract the displayed number from the number in memory.
 MR: Tap to replace the displayed number with the number in memory. If the button
has a white ring around it, there is a number stored in memory.
The stored number remains in memory when you switch between the standard and
scientific calculators.
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