Calculate Market Size (TAM/SAM/SOM)

Help me calculate market size (TAM, SAM, SOM) for [PRODUCT/SERVICE].

Context:
- What it is: [DESCRIPTION]
- Geography: [COUNTRY / REGION / GLOBAL]
- Target customer: [WHO BUYS IT]
- Price point: [APPROX ANNUAL REVENUE PER CUSTOMER]
- Competitors you know of: [LIST MAIN ONES]

Walk me through:
1. Top-down approach using industry reports and segment data
2. Bottom-up approach using customer count × price
3. TAM — total addressable market (the full opportunity)
4. SAM — serviceable addressable market (realistic segment you can reach)
5. SOM — serviceable obtainable market (realistic 3-year target)
6. Key assumptions and how to stress-test them
7. How to present this to investors credibly