I suspect that nobody knows what defines "correct math" here. It is akin to conducting an environmental impact assessment. How 'far back' do you need to go in your assessment? How many factors do you need to consider to be 'complete'? And one aspect that most folks do not consider is what assumptions (many which folks do implicitly - without really thinking about it) are made as part of the assessment? Are they 'valid' assumptions? Let's consider the case of Brewdog where they are claiming they are (or will be) carbon negative. There is no universally accepted way to confirm this really happens. How much CO2 is actually being consumed by the forest they are buying/developing? They best you could do here is some analysis of amount of CO2 consumed per acre (which may be accurate or not) and multiply by the number of acres. How much CO2 does Brewdog actually create by all f their business operations (e.g., brewing operations, distribution operations, etc.)? Again you could do some analysis, with assumptions, which may be accurate or not. I suppose folks will mostly decide to do things because they think it is a step in the right direction? Cheers!