Is this formula correct for measuring mcg like dispensaries advertise?

I have seen dispensaries advertise "100mcg" brownies and I was wondering how they came up with that number.
 
Is it as simple as 1 gram per brownie @ (ex) 15% THC = .15 micrograms?
 
I am guessing that is after the standard 25% loss that comes with making the butter from actual weight?
 
I am trying to dial in how much I am putting in to mine, and how they are getting to their numbers.

 

 
Don't need to be from a medical state my friend that is what the internet is for! I am actually confused, because if the formula is what we think there is no way this can be right. Example, they would have to put in a huge amount of grams per serving if we take the 10% THC content to get these numbers. The 100mg would need to be 10grams per serving of butter(at 10%), and there is no way that is possible IMO. If you ate 10 grams of potent butter at one time you would be so messed up it isn't even funny.
 
I make mine extremely strong with nowhere near the medical grade they use, and 2 grams is plenty. 3 you are nice for 5 hours straight.  So their 100mg is probably just 1 gram of butter per serving(not using the say 15% calculation obv), which makes a lot more sense. And yeah that is pretty weak from what I am used to.
 
http://www.leafly.com/dispensary-info/denver-relief/menu
 

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