What this step adds; in part B, sunlight and the heat it makesParts already in placeA box cooker with a 50 × 50 cm double-glazed opening (0.25 m²) and one foil reflector, on a turntable. Box cookers reach about 150 °C at most and cook at 107–135 °C (Solar Cookers International, via SHE Inc.); one with four reflectors cooked rice in 72 minutes. The heat balance here is simple and its constants are assumptions: sunlight on the glass is 900 W/m² × cos(hour angle), the reflector adds 60%, two panes and black paint keep 74% of it, and the box loses 2.2 W per °C above the 30 °C air. Empty and aimed at noon it would settle at 30 + 266 ÷ 2.2 ≈ 151 °C. Loaded with 400 g of rice in 0.8 L of water and a 1.5 L jar, each warming through its own contact with the box air (1.2 and 0.8 W/K), it passes 107 °C at 10:46, pasteurises the water (above 65 °C) at 10:58 and has the rice cooked, counted as 20 minutes above 90 °C, at 11:32. Turned on the hour to where the sun will be half an hour later, it is never more than 7.5° off. The clock runs about 1900 times fast while it heats, and waits while the cooker is turned. Drawn at 1 unit = 5 mm, from 36° up rather than 30°, so the inside of the box can be seen. This is a guide to how the parts go together, not engineering drawings. The glass, the tray and the pot pass 100 °C: lift them with dry cloths, and never look at the sun in the reflector. Pasteurising kills germs but does not remove chemicals or salt.