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Aaron Parecki

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  • Aaron Parecki https://aaronparecki.com/   •   Jul 19
    Started using the last digit of my restaurant bill as a checksum, cause I've had the tip amount changed on me too many times now

    Decide your rough desired tip, calculate your tentative total, then add up the digits before the decimal point and use that as the number of cents
    Aaron Parecki
    Total pre-tip bill: $15.90
    Rough tip: $3.00
    Pre-checksum total: $18.90
    1+8 = 9
    Final total: $18.99

    Now if someone changes the tip to $4 or $5, the checksum fails.
    Omaha, Nebraska, USA • 91°F
    Thu, Jul 19, 2018 6:12pm -05:00
    1 like 9 replies
    • Johannes Ernst
    • Daniel Reeves twitter.com/dreev
      Maybe easier version: adjust the tip so the dollars & cents of the total are equal. Then you make sure all restaurant charges on your credit card statement look like $18.18 or $7.07 or $123.23. Less subtle but realistically probably plenty subtle unless this really catches on. :)
      Sun, Mar 10, 2019 1:33am +00:00 (via brid-gy.appspot.com)
    • Derek "Nickname TBD" Rose about.me/derekrose
      I don't round down. If a gas station can charge 9/10ths of a cent per gallon the restaurant's pos should be able to go to 4 decimals.
      Fri, Jul 20, 2018 2:30am +00:00 (via brid-gy.appspot.com)
    • Torgie Madison twitter.com/torgie
      I always write the tip amount! I assumed if I didn't the cashier would have to do the math instead. Easier for 150 to do it once than one person do it 150 times. And yeah, I also decshift, round down, multiply by two. Reliably 19-20% tip, but no checksum.
      Fri, Jul 20, 2018 1:10am +00:00 (via brid-gy.appspot.com)
    • Aaron Parecki aaronparecki.com
      you write the tip amount on the receipt? I just always write the total amount.
      Fri, Jul 20, 2018 12:47am +00:00 (via brid-gy.appspot.com)
    • Derek "Nickname TBD" Rose about.me/derekrose
      My algorhythm for tipping prioritises speed so I just allow for a margin of error. We can adjust for it in the mapreduce before cold storage. And I try to obfuscate the tip to prevent alterations. So far so good.

      Left shift decimal 1 place the multiply by 2.
      Fri, Jul 20, 2018 12:44am +00:00 (via brid-gy.appspot.com)
    • Torgie Madison twitter.com/torgie
      This gets tricky when prices are either large or end in strange decimals (sales tax):

      Pre-tip bill: $81.12
      Rough tip: $16
      Pre-checksum total: $97.12
      9 + 7 = 16 (?)
      Final: $97.16 (last digit of sum = 6)

      Adjust up to $16.04 or down to $15.94? The mental math could trip people up.
      Fri, Jul 20, 2018 12:36am +00:00 (via brid-gy.appspot.com)
    • Kelly Clowers www.clowersnet.net/~krc
      :-O
      Fri, Jul 20, 2018 12:26am +00:00 (via brid-gy.appspot.com)
    • Aaron Parecki aaronparecki.com
      That was a bad example. Last time this happened, my $5 tip was changed to a $15 tip.
      Thu, Jul 19, 2018 11:53pm +00:00 (via brid-gy.appspot.com)
    • Kelly Clowers www.clowersnet.net/~krc
      why? Unless they change it to like 100% or something wild, let em have it. Likely they need it if they go to the trouble
      Thu, Jul 19, 2018 11:16pm +00:00 (via brid-gy.appspot.com)
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Hi, I'm Aaron Parecki, Director of Identity Standards at Okta, and co-founder of IndieWebCamp. I maintain oauth.net, write and consult about OAuth, and participate in the OAuth Working Group at the IETF. I also help people learn about video production and livestreaming. (detailed bio)

I've been tracking my location since 2008 and I wrote 100 songs in 100 days. I've spoken at conferences around the world about owning your data, OAuth, quantified self, and explained why R is a vowel. Read more.

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