> I have a 4 digit postcode, I have to look it up every time I have to fill in an address form for delivery.

> A code sounds foolproof, until you realise most people don't engage with them for most of their lives - you don't tell the uber driver the zip/post code you are waiting in, and travelling to, nobody does.

When the above comments said +4, they meant knowing the second half of the nine digit zip code.

Basically everyone in the US knows the first 5 digits. It's really easy to memorize them. If you can remember your city, you can remember your zip code. And in the US you use it all the time, so it stays memorized.

> edit: just to add - Magic numbers are bad. Software engineers know that a number that's undocumented in code is unmaintainable, a zip code is worse.

That complaint about magic numbers is completely off base. Magic strings are just as bad in software. "Beverly Hills" and 90210 are equal sins on the magic front.

Your zip plus 4 changes. It isn't worth trying to know as it isn't supposed to be constlnt. If you send a lot of mail there is a discount for using it but you have to update everyone's address often (iirt at least 4x per year)