Metrics and measurement

[Mia - I'm starting with some big questions because it's an area I know nothing about.]

The technical approaches

API keys, logs, whatever - what works best? If the answer is 'it depends', what does it depend on?

The business requirements

Funders, managers, boards, marketing - what do we need to provide to whom? How comparable to previous metrics and stats does it need to be? How much explanation or help with interpretation is required?