Nanotechnology ethics keeps circling back to one hard, quantitative question: given real toxicology uncertainty, how conservative should a legal exposure limit be? This simulator makes the regulatory-science machinery visible on a pannable, zoomable 2D log-scale chart. Drag a rodent study's NOAEL through the standard chain of uncertainty factors — interspecies extrapolation, human variability, database gaps, and a precautionary modifying factor — and watch a log-scale staircase descend from the raw animal result to the actual permissible exposure limit. A glowing 250-particle swarm renders the population's own biological variability as a log-normal distribution of individual sensitivity thresholds, so instead of an abstract multiplier you see, particle by particle, what fraction of real people the chosen limit protects — and watch that fraction collapse the moment real-world exposure creeps above it.