Tradespeople still carry physical levels for critical measurements where smartphone apps lack accuracy. A digital level app could replace this tool with professional-grade calibration, angle memory, and industry-specific presets (like roof pitches or machine alignments).
Charge contractors and workshops via one-time purchase or subscription for advanced features. The app should work offline and sync data to cloud for teams.
Start with core level functionality plus one vertical (e.g., woodworking angles), then expand to other trades. The biggest risk is hardware limitations - not all phone sensors are equally precise.