[Lex Computer & Tech Group/LCTG] accuracy

[Paul Garmon]

On Sun, Sep 20, 2020 at 4:47 PM john rudy <jjrudy1 at comcast.net> wrote:

> I just purchased an item from Amazon.
>
> Their accuracy is astounding.
>
>
>
>
First off: Accuracy and Precision
<https://www.mathsisfun.com/accuracy-precision.html> (so, precision is a
closer match to just having more digits, as was already pointed out). Second

Maybe they were just using one of the old Pentiums, so it's wrong after a
few decimal digits anyway?   ;->

   - see: Pentium FDIV bug - Wikipedia
   <https://en.wikipedia.org/wiki/Pentium_FDIV_bug#:~:text=The%20Pentium%20FDIV%20bug%20is,the%20early%20Intel%20Pentium%20processors.&text=The%20bug%20was%20discovered%20in,the%20floating%2Dpoint%20division%20circuitry.>

   - How a Minor Calculation Error Cost Intel Half a Billion Dollars
   <https://www.vice.com/en_us/article/dyzqdj/how-a-minor-calculation-error-cost-intel-half-a-billion-dollars>


   The presence of the bug can be checked manually by performing the
   following calculation in any application that uses native floating point
   numbers, including the Windows Calculator
   <https://en.wikipedia.org/wiki/Calculator_(Windows)> or Microsoft Excel
   <https://en.wikipedia.org/wiki/Microsoft_Excel> in Windows 95
   <https://en.wikipedia.org/wiki/Windows_95>/98
   <https://en.wikipedia.org/wiki/Windows_98>.

   The correct value is:
   {\displaystyle \textstyle {\frac
   {4,195,835}{3,145,727}}=1.333820449136241002}[image: \textstyle {\frac
   {4,195,835}{3,145,727}}=1.333820449136241002]


   When converted to the hexadecimal value used by the processor, 4,195,835
   = 0x4005FB and 3,145,727 = 0x2FFFFF. The '5' in 0x4005FB triggers the fault
   in the FPU control logic. As a result, the value returned by a flawed
   Pentium processor in certain situations is incorrect at or beyond four
   digits:[11] <https://en.wikipedia.org/wiki/Pentium_FDIV_bug#cite_note-11>
   [12] <https://en.wikipedia.org/wiki/Pentium_FDIV_bug#cite_note-12>
   {\displaystyle \textstyle {\frac {4,195,835}{3,145,727}}=1.333{\color
   {Red}{739068902037589}}}[image: \textstyle {\frac
   {4,195,835}{3,145,727}}=1.333{\color {Red}{739068902037589}}]



This "package weight to the nth decimal digit" reminds me of something that
happened a few years ago with Amazon shipping.  I had ordered an audio
recording computer interface on a Wednesday morning, needed for that
weekend. I specified ONE DAY DELIVERY and paid extra.  Figured it would be
delivered either Thursday or (at worst) Friday, providing some time to set
it up for Saturday. Well, when I checked on the delivery status early
Thursday morning, Amazon reported the item was shipped UPS Ground with a
TWO WEEK SHIPPING window.  Being critically important, I
immediately ordered the same item from a place called SameDayMusic
<https://www.samedaymusic.com/>, for considerably more money (and that
arrived on Friday, so the weekend was saved!). Meanwhile, I went to cancel
the Amazon order, but they would not let me, since the item had not yet
arrived. When the Amazon unit finally arrived the next week (ahead of their
schedule), I went to return it, but they charged me for the ("no good
reason") return, since it was delivered well within the time they said. I
attempted to explain why it was late, but they kept saying "we see it
arrived within the two weeks we allowed".  Saying that I had ordered it
with one day delivery just didn't register with them, as it no longer
showed on the order that way, so they didn't believe me. I figured it would
never be resolved and I would just be out the return shipping (this was
before I had Amazon Prime, so I think it was about $15). Well, a few weeks
later, I noticed a news story saying that Amazon had formed a special
executive group to deal with "things gone wrong" there, so I contacted
them. Took a few weeks to investigate, but in this case, they figured out
what happened, which was this: when an item would arrive in Amazon
shipping, they would weigh it, and if it didn't match the weight listed in
their database, they would change the shipping to ground instead of
whatever had been specified (including overnight).  Probably, they should
have just flagged the item in their database for review and shipped it as
ordered, but that wasn't the procedure. They eventually refunded me the
return shipping and also gave me a $50 gift certificate (and hopefully
adjusted their shipping process).

Paul
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