Circular Reasoning: the Time-traveling Computer

From Wikipedia:

Let's suppose there is a computer that can communicate with itself both in the past and in the future. The computer calls up its future self:

Computer: [12:00] Hello there. What's the answer to this really tough problem?
Future Computer: [12:05] It's 16 widgets.
Computer: [12:01] Great, thank you! (Hangs up) Let me check if this is correct... Yes it is! (Phone rings)
Past Computer: [12:00] Hello there. What's the answer to this really tough problem?
Computer: [12:05] It's 16 widgets.
Past Computer: [12:01] Great, thank you!

How does Future Computer know the answer? Think about it!