Laundry: laundering
Accounts registers: _
Pretty sure the teller screwed up my transaction yesterday, withdrew cash from one account and instead of depositing it to the other, redeposited it back to the same account.
Also, I received my PIN mailer for my credit union debit card. At some point I'll probably get it re-PINned, but meanwhile I learned a simple math trick one can use to write a PIN reminder on one's card without exposing the PIN itself.
First, you choose a "master PIN", one which you never have to write down because it could only be dislodged from your memory by serious brain damage. And if that happens, you'll have bigger issues than being able to use ATMs for a while anyway.
Then by modular subtraction (that's like "real" subtraction, but without any "borrowing" or "carrying") you derive a PIN offset. This PIN offset is what you write on your card. And THEN, when you're at the ATM and need to enter the PIN associated with that card, you look at this offset you wrote on the card, and use modular addition with your master PIN to recover that card's real PIN.
So let's say you chose 5857 as your master PIN, because that was the last 4 digits of your mom's phone number when you were growing up so it was drilled into your brain in every public restroom wall in the tri-county area. And let's say your card's assigned PIN is 8368. By modular subtraction we get a PIN offset of (8368-5857)=3511. See how we didn't "borrow" from the thousands place, when we subtracted 8 from 3 in the hundreds place? So you write this PIN offset, 3511, on your card.
Now when you're at the ATM at 4:45AM on a Tuesday morning, annoyingly half-sober and only getting moreso, you whip out your card and can't remember the PIN; so you look at the number you wrote on the card. You use modular addition, which simply discards any "carried" digits, to sum the number written on the card with your unforgettable super PIN: 3511+5857=8368. See how we didn't "carry the one" when we added 5 and 8 in the hundreds place? If the sum in any place gives a result greater than 9, you discard the tens-place, keeping only the ones-place. This lets you calculate each digit, key it in, and move on to the next calculation, in your state of moderately restricted cognitive capacity.
An extreme example to demonstrate how using modular arithmetic instead of "real" addition and subtraction lets you sidestep awkward negative results and place-carrying: your master PIN is 8642, your card PIN is 4321. So the PIN offset you'd write on your card is 4321-8642=6789, and at the ATM you'd modular-add 6789+8642, to key in the result 4321.
The only way you can really screw this up is if you don't understand the simple math AT ALL, and reverse the order in the initial mod-subtraction operation. It's card PIN minus master PIN, not vice versa. If you subtract in the wrong order then you're boned, because the result is only useful for recovering your master PIN by knowing the card PIN... and of course that's completely not useful at all. Using our first example, if ur doin it wrong, you'd mod-subtract (5857-8368)=7599, and when you're standing at the ATM ready to key in the card PIN, you'd mod-add this incorrect PIN offset you wrote on your card to your unforgettable master PIN, 7599+5857 and get 2346... which obviously isn't going to help you buy malt liquor. Easy mnemonic to keep that sorted: "card" comes before "master" alphabetically.
"So Remember:
Card PIN Minus Super Master PIN,
Don't Be That Stupid Bastard PIN!"