RISKS-LIST: Risks-Forum Digest Sunday 9 May 2009 Volume 25 : Issue 66
Date: Wed, 6 May 2009 11:46:47 -0700
Subject: Strange cash register arithmetic favors the house
Yesterday I noticed an item on sale for a great price so I picked up
four and proceeded to the checkout. When the cashier rung up the items
oddly the fourth was charged at the non sale price. We quickly surmised
that there was probably a limit of three available at the sale price.
Since I wasn't interested in paying the normal price for the fourth item,
I asked to take that one back. Normally this is a quick routine matter.
The cashier voids the item by hitting a key on the cash register and
then re-scans the item to deduct it from the tab. What happened next
was bizarre. Instead of deducting the normal price of $3.49 that I was
charged, it deducted the sale price of $1.88. Hmmm.... I was assuming
that the register would have used a stack model, removing the last item
that had transacted at $3.49. Maybe the register software was using
FIFO instead ? Then it got more surreal.
Fortunately no-one was waiting in line so the cashier voided the other
3 items, hoping to clear the FIFO. But all 4 items deducted the sale
price of $1.88 from the total. None of them deducted the normal price
of $3.49. So here we have the strange arithmetic of
A+B+C+D - (A+B+C+D) > 0. In fact if the cash register software is to be
believed $0.00 = $1.61 which is the amount remaining on the cash
register that I would pay for a null basket.
The only way out was to void the entire transaction (which required the
manager to intervene) and start over. So here we have a state machine
that enables easy access to an unfavorable state (overpaying for a item)
but difficult to transition back out to the favored state (because
the manager is required). This creates something of a trap that will
result in some customers overpaying. If you make the mistake of bring
sale items that exceed the limit (easy to do since the limit was not
posted), you will overpay unless you and the cashier take these actions :
1) Notice the overcharge (I would have missed this had the cashier
not been alert)
2) Notice that voiding an item does not remove the overcharge and/or :
3) Call a manager to void the entire transaction
This occurred at a large USA retail chain with thousands of stores and
millions of customers. This retailer stands to reap a windfall profit
from customers who don't notice that they are being overcharged.
If a similar situation occurred in casino gaming machines you can bet
that regulators would become quickly involved.
> RISKS-LIST: Risks-Forum Digest Sunday 9 May 2009 Volume 25 : Issue 66
>
> Date: Wed, 6 May 2009 11:46:47 -0700
> Subject: Strange cash register arithmetic favors the house
>
> Yesterday I noticed an item on sale for a great price so I picked up
> four and proceeded to the checkout. When the cashier rung up the items
> oddly the fourth was charged at the non sale price. We quickly surmised
> that there was probably a limit of three available at the sale price.
>
> Since I wasn't interested in paying the normal price for the fourth item,
> I asked to take that one back. Normally this is a quick routine matter.
> The cashier voids the item by hitting a key on the cash register and
> then re-scans the item to deduct it from the tab. What happened next
> was bizarre. Instead of deducting the normal price of $3.49 that I was
> charged, it deducted the sale price of $1.88. Hmmm.... I was assuming
> that the register would have used a stack model, removing the last item
> that had transacted at $3.49. Maybe the register software was using
> FIFO instead ? Then it got more surreal.
>
> Fortunately no-one was waiting in line so the cashier voided the other
> 3 items, hoping to clear the FIFO. But all 4 items deducted the sale
> price of $1.88 from the total. None of them deducted the normal price
> of $3.49. So here we have the strange arithmetic of
> A+B+C+D - (A+B+C+D) > 0. In fact if the cash register software is to be
> believed $0.00 = $1.61 which is the amount remaining on the cash
> register that I would pay for a null basket.
>
> The only way out was to void the entire transaction (which required the
> manager to intervene) and start over. So here we have a state machine
> that enables easy access to an unfavorable state (overpaying for a item)
> but difficult to transition back out to the favored state (because
> the manager is required). This creates something of a trap that will
> result in some customers overpaying. If you make the mistake of bring
> sale items that exceed the limit (easy to do since the limit was not
> posted), you will overpay unless you and the cashier take these actions :
>
> 1) Notice the overcharge (I would have missed this had the cashier
> not been alert)
>
> 2) Notice that voiding an item does not remove the overcharge and/or :
>
> 3) Call a manager to void the entire transaction
>
> This occurred at a large USA retail chain with thousands of stores and
> millions of customers. This retailer stands to reap a windfall profit
> from customers who don't notice that they are being overcharged.
>
> If a similar situation occurred in casino gaming machines you can bet
> that regulators would become quickly involved.
thanks for sharing. Let's all learn from others.
It's an educational system . I can believe in.
--
It's amazing what you can do. If...
you put your mind to it.
> RISKS-LIST: Risks-Forum Digest Sunday 9 May 2009 Volume 25 : Issue 66
> Date: Wed, 6 May 2009 11:46:47 -0700
> Subject: Strange cash register arithmetic favors the house
> Yesterday I noticed an item on sale for a great price so I picked up
> four and proceeded to the checkout. When the cashier rung up the items
> oddly the fourth was charged at the non sale price. We quickly surmised
> that there was probably a limit of three available at the sale price.
> Since I wasn't interested in paying the normal price for the fourth item,
> I asked to take that one back. Normally this is a quick routine matter.
> The cashier voids the item by hitting a key on the cash register and
> then re-scans the item to deduct it from the tab. What happened next
> was bizarre. Instead of deducting the normal price of $3.49 that I was
> charged, it deducted the sale price of $1.88. Hmmm.... I was assuming
> that the register would have used a stack model, removing the last item
> that had transacted at $3.49. Maybe the register software was using
> FIFO instead ? Then it got more surreal.
> Fortunately no-one was waiting in line so the cashier voided the other
> 3 items, hoping to clear the FIFO. But all 4 items deducted the sale
> price of $1.88 from the total. None of them deducted the normal price
> of $3.49. So here we have the strange arithmetic of
> A+B+C+D - (A+B+C+D) > 0. In fact if the cash register software is to be
> believed $0.00 = $1.61 which is the amount remaining on the cash
> register that I would pay for a null basket.
> The only way out was to void the entire transaction (which required the
> manager to intervene) and start over. So here we have a state machine
> that enables easy access to an unfavorable state (overpaying for a item)
> but difficult to transition back out to the favored state (because
> the manager is required). This creates something of a trap that will
> result in some customers overpaying. If you make the mistake of bring
> sale items that exceed the limit (easy to do since the limit was not
> posted), you will overpay unless you and the cashier take these actions :
> 1) Notice the overcharge (I would have missed this had the cashier
> not been alert)
> 2) Notice that voiding an item does not remove the overcharge and/or :
> 3) Call a manager to void the entire transaction
> This occurred at a large USA retail chain with thousands of stores and
> millions of customers. This retailer stands to reap a windfall profit
> from customers who don't notice that they are being overcharged.
> If a similar situation occurred in casino gaming machines you can bet
> that regulators would become quickly involved.
Have experienced this several times, but only at WalMart.
skarkada@gmail.com wrote:
> Interesting, but it could as well be due to handy work of a sloppy programmer.
In fact that is precisely what it is.
XML site map
>
> Date: Wed, 6 May 2009 11:46:47 -0700
> Subject: Strange cash register arithmetic favors the house
>
> Yesterday I noticed an item on sale for a great price so I picked up
> four and proceeded to the checkout. When the cashier rung up the items
> oddly the fourth was charged at the non sale price. We quickly surmised
> that there was probably a limit of three available at the sale price.
>
> Since I wasn't interested in paying the normal price for the fourth item,
> I asked to take that one back. Normally this is a quick routine matter.
> The cashier voids the item by hitting a key on the cash register and
> then re-scans the item to deduct it from the tab. What happened next
> was bizarre. Instead of deducting the normal price of $3.49 that I was
> charged, it deducted the sale price of $1.88. Hmmm.... I was assuming
> that the register would have used a stack model, removing the last item
> that had transacted at $3.49. Maybe the register software was using
> FIFO instead ? Then it got more surreal.
>
> Fortunately no-one was waiting in line so the cashier voided the other
> 3 items, hoping to clear the FIFO. But all 4 items deducted the sale
> price of $1.88 from the total. None of them deducted the normal price
> of $3.49. So here we have the strange arithmetic of
> A+B+C+D - (A+B+C+D) > 0. In fact if the cash register software is to be
> believed $0.00 = $1.61 which is the amount remaining on the cash
> register that I would pay for a null basket.
>
> The only way out was to void the entire transaction (which required the
> manager to intervene) and start over. So here we have a state machine
> that enables easy access to an unfavorable state (overpaying for a item)
> but difficult to transition back out to the favored state (because
> the manager is required). This creates something of a trap that will
> result in some customers overpaying. If you make the mistake of bring
> sale items that exceed the limit (easy to do since the limit was not
> posted), you will overpay unless you and the cashier take these actions :
>
> 1) Notice the overcharge (I would have missed this had the cashier
> not been alert)
>
> 2) Notice that voiding an item does not remove the overcharge and/or :
>
> 3) Call a manager to void the entire transaction
>
> This occurred at a large USA retail chain with thousands of stores and
> millions of customers. This retailer stands to reap a windfall profit
> from customers who don't notice that they are being overcharged.
>
> If a similar situation occurred in casino gaming machines you can bet
> that regulators would become quickly involved.