Three dials on the same camera — and only two of them are actually settings you dial in.
Ask most people sizing an NVR how much storage a camera needs, and they'll reach for a simple formula: resolution × frame rate × some fixed bits-per-pixel number. It feels rigorous — it has units, it multiplies clean numbers together — and it's wrong in a way that can throw a storage estimate off by several times. Resolution and frame rate are settings you choose. Bitrate— the thing that actually determines how much data hits the disk every second — is not simply derived from those two settings. It's also driven by something neither setting controls at all: how much the scene in front of the camera is actually changing, frame to frame.