A Shock Level measures the high-tech concepts you can contemplate without being impressed, frightened, blindly enthusiastic—without exhibiting future shock. Shock Level Zero or SL0, for example, is modern technology and the modern-day world, SL1 is virtual reality or an ecommerce-based economy, SL2 is interstellar travel, medical immortality or genetic engineering, SL3 is nanotech or human-equivalent AI, and SL4 is the Singularity.
From Future Shock Levels (1999):