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When using a point of sales system or a payment terminal, when entering a sum, why are cents entered first? In example, when typing '99', you would be entering a sum of '0.99$' not '99.0$'.
Is there a name for this kind of a notation? Where does the system originate from?
It's not true that amounts are entered right to left, rather what the cashier is typing is the value of the item in cents. If the cashier wants to enter the item price $12.50, they type 1, 2, 5, 0, from left to right. The advantage of entering prices in cents is that the cashier would not have to type the decimal dots.
What you are really seeing is simply the result of the mini display being right aligned. As a result, as the cashier type more digits, the digits previously entered get pushed to the left.
One of the reason the mini display are right-aligned is because many cashier machines uses seven-segment display, and usually the position of the dot is fixed in the display. If the display are left-aligned, the display would have to add decimal dots between all digits instead of just having one.
An observation is that this pattern leans on the side of least impact on consumer. Let's say as a user I want to donate to someone $0.50 . There would a big problem if the input defaulted to $50.00 as it expected me to put in a decimal.
Now most likely this would not happen often but it would make a headache if even 1% of your users ran into this issue. With cents entered first the impact would be the user donated too little.
At Royal Bank of Canada when you deposit money it starts cents but when you withdraw it starts with dollars as you can't with draw cents.
So in my opinion go the route of least impactful design for your edge case users.
Also note that if you do implement dollars first, your make it so users must put decimal or they need to click into input field or masking area to input decimals. I am not seeing any downside to using cents first unless of course your situation causes the users to never need to interact with that denomination.
