Confused about the Luhn algorithm

I’m working on the credit card checker now (Credit Card Checker) and I’m confused about the general Luhn algorithm, since in the Wikipedia page linked here. It says that it’s supposed to include the rightmost number, but according to the provided diagram on this website. It shows that we’re not supposed to include it. I don’t know whether if there’s an error or I’m misunderstanding something. Any clarification would be highly appreciated.

Thinking critically: what are the differences between including and excluding the rightmost number? (Try by hand). Do they affect validation? Which one makes more sense?

Here’s one link.

Another thought: check the patent → US2950048A - Computer for verifying numbers - Google Patents

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Thank you so much for the response and resources. I think I’m getting it now, just not 100% but maybe that just comes with time.

It’s not you that’s misunderstanding. Like many things on Codecademy, the content and description of the activity is confusing.