So I'm just getting into the workshop, and couldn't find the equation for item earnings anywhere, so I decided to make a little excel sheet and figure it out myself. Here's what it's looking like after a few days

Expected:
Earnings = Value * Popularity modifier * Supply modifier

Reality:
With the same Popularity and Supply, the % boost to earnings can vary

Some of my sample size involves a reading after multiple of the same item were made, so I divided the total by that number. After making even more of that item in the same day, the average earnings dropped even more. I looked at the chart, and it had decreasing Demand Shift

Theory:
Demand Shift isn't a predictor of future demand; it's how the earnings will change with each production
  • Increasing/Skyrocketing - each production pays more than the last
  • None - earnings stays the same no matter how many you make
  • Decreasing/Plummeting - each production pays less than the last

So my current working theory is:
Earnings = Value * (Popularity/Supply modifier) + (Demand Shift modifier * amount of item already produced)

I'm going for the 17,000 cowries achievement this week, so it'll be next week before I can really get into the weeds experimenting, and it'll be the weekend before I can be home to check every few hours to properly measure the experiment