Which numeric keypad layout (PC or register) should be used for a touch panel?

Question

We lately had a usability test for a self-service payment machine. It's very similar to the e-banking process.

The whole banking process is over a touchscreen until they enter the debit card. The system then switches to the card terminal.

The keyboard for entering an account number during the accounting process on the touchscreen is the same layout as PC keyboards have? 3x3 starting with 789 on top and 0 separate in the middle of the 4th row.

The keyboard used by the card terminal is the same as for registers or telephones: 3x3 starting with 123 on top and 0 separate in the middle of the 4th row.

During the test only one user mentioned that the layout is different. But I'm now curious why those things have different layouts and whether we should switch the layout for the touchscreen input to the same as the card terminal. That would give some consistency. On the other hand a PC number pad is more consistent with the usually known input during e-banking.

We only can change the touchscreen UI.

Addendum

I've found a page which explains a lot of the history of these number-pad formats.

So I think the “why” is pretty well explained. But the main question still remains: should there either be some consistency with the e-banking or with the card terminal for a self-service machine?

I've checked some other self-service terminals, including ones for tickets at the bus station. But those don't operate with just numbers, but mainly with text. Therefore they just have standard alphanumeric keyboards.

Answer 1

Fix the screen layout to match the physical number pad it will be used with. If the software will never used along with a computer keyboard, there is no reason to mimic it.

You say only one user mentioned the issue, but you don't say how many users you were testing with. If you were doing an informal (five-user) usability survey, you should take all comments seriously.

While most users may not notice the difference, those who do will privately snicker at the designer (you). Admit it. Whenever you encounter bad designs, you think, "I would have done better." Here's your chance. Do better.

Also, suppose the number pads had matched initially. Would you expect that all the other users to would have commented that the number pads should have been made to not match? While no one will fault you for having attention to detail and designing a consistent interface. You will be faulted for designing an inconsistent interface.