When entering currency amounts into an input field, I've seen two methods:
Keyed Decimal: The keypad includes the decimal character and the user enters the decimal along with the numbers. The Chase mobile app uses this approach.
Key Display 5 $5 4 $54 . $54. 6 $54.6 3 $54.63
Fixed Decimal: The keypad excludes the decimal character and the numbers fill around a fixed decimal. The PayPal and Square mobile apps both use this approach.
Key Display 5 $0.05 4 $0.54 6 $5.46 3 $54.63
The keyed decimal approach seems more straightforward to me, and it also requires 2 fewer keystrokes when entering non-decimal amounts (e.g. $10 only requires typing 1-0, instead of 1-0-0-0). However, users of our payment processing app have accidentally charged amounts like $123,456.00 instead of $1,234.56 because they were expecting a fixed decimal interaction instead of a keyed decimal interaction.
Is this just a matter of preference, or are there other merits to a fixed decimal approach that I may be overlooking?