How does the karma scoring mechanism work on Reddit?

Surprisingly, upvotes and downvotes have different values when calculating karma
Reddit user shared his research into the mechanics of counting votes to determine karma on social media posts. And the results were surprising: upvotes and downvotes are not equal to each other in a 1:1 ratio.

For example, a post with 40,000 upvotes didn't actually earn the user 40,000 karma, but about 4,000.

• Here's how it works:
  
  The first time after publishing a post is the most important - each upvote counts towards karma 1:1;
  
  The subsequent ones are not so valuable - the more upvotes, the less karma each subsequent vote adds;
  
  The age of the post is important: as it ages, the same number of upvotes will be counted less towards karma;
  
  The subreddit where the post is published also matters, but the connection is not entirely clear yet;
  
  The maximum karma you can get from one post is 8,000.

Where are you getting this information from?