Was a pain to find in the article but according to them, 1 cannabis unit is 5mg of THC. And they recommend no more than 8 per week, or 40mg. I didn't read the entire paper so take my commentary with a grain of salt.

I think there may be a bit of a hole in this methodology because of different consumption methods. For example, smoking a regular joint vs putting that same amount of flower in a dry vape. Or dietary factors that could increase or decrease thc absorption for edibles.

Even accounting for that, 40mg of THC is not a lot. A half gram joint at 10% thc would exceed that. Seems like these guidelines are incredibly conservative.