How many tiers does the monitoring approach describe?

1. The tiers run from the whole organisation down to one system. 2. They are organisation, business processes and information systems. 3. Tier 1 is organization, Tier 2 is mission and business processes, and Tier 3 is information systems. 4. So the answer is three. _Source: NIST SP 800-137, 'Information Security Continuous Monitoring for Federal Information Systems and Organizations'_