Fig. 1.

Four 30 s epochs originally published in the Rechtshaffen and Kales manual demonstrating the change from N2 sleep to N3sleep based on % of delta EEG waves [11]. Underlining indicates delta waves that met 75 uv. amplitude and 0.2–2.0 frequency. The top tracing appears in Figure 14 The other tracings appear in Fig. 2. The first 2 tracings have less than 20% delta EEG and are thus scored as Stage 2. The second 2 tracings have more than 20% delta EEG and are thus scored as stage 3.