# Methods and measurement notes

## Why one-step error and not video PSNR?

H3's sampler is chaotic: computing only the AdaLN in fp32 instead of bf16 already moves a 20-step clip to
~17 dB PSNR against the shipped model. End-of-run pixel metrics therefore cannot rank recipes. Each recipe is
instead fed the exact recorded inputs of every step and compared with the BF16 output of that step.

## Measurement notes

- **Noise floor ~1–2%.** Replays are bitwise exact within one container but differ by 1–2% across GPU hosts, and
  any bf16-level change lands at that level. Compare recipes within a run; each run reports its own floor.
- **Size** is the approximate transformer checkpoint size with the rank-12 AdaLN (NVFP4 counted as 4.5 bits per
  weight including block scales).
- **Simulation vs ComfyUI.** NVFP4 activation rounding is implementation-defined: ComfyUI's CUDA and Triton kernels
  agree with each other but differ from ModelOpt's simulation by ~2% on a quantized activation. Rankings should
  carry over; final quality is judged in ComfyUI itself (below).