Designed by Christopher Wren in 1675 for Astronomer Royal John Flamsteed, Flamsteed House sits atop Greenwich Hill. Inlaid across the courtyard is the Prime Meridian Line (0° 0' 0" longitude), dividing the Western and Eastern Hemispheres of Earth.
The full decipherment and its observational protocol — where to stand, when, and what to watch for — are in the London field codex.
Or read the complete Florence codex free first.