This debate on the Fred Wilson blog whether you should look at Twitter in terms of monthly active users who log in, or (the much larger number of) people who view/get exposed to tweets is an important lesson in investor presentation design: sometimes you need to educate your audience how to think about you.
Investors like benchmarks that they can compare quickly across stocks, like features of car: EPS, CAC, churn, MAU, eye balls, beta, EV/EBITDA. If your company does not fit the traditional pattern you need to make sure your audience understands it.
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