4 ms·

7kb for a supermarket bill is plenty, and you can have several of them. Forms and legal documents should all have an immutable official url and uuid anyway to

7kb for a supermarket bill is plenty, and you can have several of them. Forms and legal documents should all have an immutable official url and uuid anyway to point to their legal and administrative context.

michaelt 7y ago
The largest QR code in the standard, "version 40" - can only store 3 kilobytes at the lowest level of error correction and 1.2 kilobytes at the highest level [1]. And that's a pretty huge QR code [2] My back-of-the-envelope calculations say you'd need 61 bits per line on a receipt just to encode UPC, quantity and price. So the largest QR code would only allow 19-50 lines. And that's without including data like the store name, special offers, means of payment and so on. Believe me, plenty of people buy more than 50 items in their supermarket christmas shop :) Standardised digital receipts would be neat but, QR codes encoding the data ain't the way to go about it. [1] https://www.qrcode.com/en/about/version.html https://www.qrcode.com/en/about/version.html [2] https://commons.wikimedia.org/wiki/File:Qr-code-ver-40.svg https://commons.wikimedia.org/wiki/File:Qr-code-ver-40.svg
- smegger001 7y ago
  it could just contain a url linking to a page with to content.
- jlgaddis 7y ago
  Seems like the obvious thing would be to have the QR code contain a "receipt ID" (UUID?) in a URL. When the QR code is scanned, the browser opens to the URL, the remote side takes your "receipt ID", and presents you with a list of all the items you purchased. I can't imagine any decent-sized retailer isn't already maintaining records like this.
  - naniwaduni 7y ago
    See, one of the useful properties of a paper receipt is that, once you receive it, you can be fairly confident about the ~one way you're going to lose it
    - jmiserez 7y ago
      Two ways. Receipts fade, sometimes very quickly.
- tzs 7y ago
  1.2 kilobytes = 9.6 kilobits. If you need 61 bits per line, you’ve got enough bits for 157 lines. 393 lines if we go with 3 kilobytes. I think you may have used 61 bytes per line in your calculation rather than 61 bits.
  - colejohnson66 7y ago
    I (not OP) would say bytes would be closer. The product name could be 20 characters long (20 bytes minimum)
    - tzs 7y ago
      OP was assuming the receipt would list the product UPC code rather than product name. A UPC code is 12 digits, which can be encoded in 40 bits.

michaelt 7y ago

The largest QR code in the standard, "version 40" - can only store 3 kilobytes at the lowest level of error correction and 1.2 kilobytes at the highest level [1]. And that's a pretty huge QR code [2] My back-of-the-envelope calculations say you'd need 61 bits per line on a receipt just to encode UPC, quantity and price. So the largest QR code would only allow 19-50 lines. And that's without including data like the store name, special offers, means of payment and so on. Believe me, plenty of people buy more than 50 items in their supermarket christmas shop :) Standardised digital receipts would be neat but, QR codes encoding the data ain't the way to go about it. [1] https://www.qrcode.com/en/about/version.html https://www.qrcode.com/en/about/version.html [2] https://commons.wikimedia.org/wiki/File:Qr-code-ver-40.svg https://commons.wikimedia.org/wiki/File:Qr-code-ver-40.svg

smegger001 7y ago
it could just contain a url linking to a page with to content.
jlgaddis 7y ago
Seems like the obvious thing would be to have the QR code contain a "receipt ID" (UUID?) in a URL. When the QR code is scanned, the browser opens to the URL, the remote side takes your "receipt ID", and presents you with a list of all the items you purchased. I can't imagine any decent-sized retailer isn't already maintaining records like this.
- naniwaduni 7y ago
  See, one of the useful properties of a paper receipt is that, once you receive it, you can be fairly confident about the ~one way you're going to lose it
  - jmiserez 7y ago
    Two ways. Receipts fade, sometimes very quickly.
tzs 7y ago
1.2 kilobytes = 9.6 kilobits. If you need 61 bits per line, you’ve got enough bits for 157 lines. 393 lines if we go with 3 kilobytes. I think you may have used 61 bytes per line in your calculation rather than 61 bits.
- colejohnson66 7y ago
  I (not OP) would say bytes would be closer. The product name could be 20 characters long (20 bytes minimum)
  - tzs 7y ago
    OP was assuming the receipt would list the product UPC code rather than product name. A UPC code is 12 digits, which can be encoded in 40 bits.