The final test of the new instrument took place in Entry hall 730: The Grand Drop Well of the Outer Defenses. This was a circular upright tower sixty arm-lengths wide, carved straight through the dark rock bedrock. It dropped one hundred and sixty deep-water lengths from the lower foundation of the foundries down to the bedrock sump of the Submerged Bastions.
Overhead, mounted on a heavy bronze overhead frame across the mouth of the well, sat a three-foot bronze pulley wheel, fitted with ball bearings and lined with hardened rubber to prevent cord wear. Standing beside the pulley wheel was the manual winding drum, geared to a hand-crank that allowed three thousand feet of line to be hauled smoothly by a single land-mapper.
Qiao Ming stood at the edge of the drop well, his bare horn-hard feet gripping the wet andesite rim. He hitched his oilskin coat tighter across his chest, feeling the new True-Sight Verdigris Needle resting securely in its sheath over his heart. In his hands, he held the eight-sided lead line-weight, its bronze mid-air loop coupled to the thimble of the newly marked star-thread line.
Behind him, Yan Zhiqiu stood at the brake lever of the winding drum, her lantern lighting up the depth counter. Her face was calm, attentive, and filled with quiet excitement. “The well descends one hundred and sixty deep-water lengths to the underwater keel drain pits,” she announced. “The water level begins at Fathom Ninety. The lower seventy deep-water lengths are sunk under…
