He returned to the manual. Page 4-17: It described a phenomenon called settling error —a phantom offset caused by the gyro aligning not to true north, but to a plane of rotation influenced by the ship’s own course changes. The cure was a "latitude damping" reset. He performed it. The display flickered, reset, and returned to 271.3.

It was subtle. On a clear night with Polaris pinned to the sky, Saito took a sextant sight. The CMZ 700 read 271.3 degrees. The star said 270.0. A full degree off.

Tanaka nodded, unimpressed. "So, like a GPS."

Tanaka came up with coffee. "Captain? The auto-helm is acting strange. It keeps trying to correct two degrees to port."

"This instrument is designed to find north. It is not designed to understand why north moves."

Page 1-2: "The CMZ 700 utilizes a dynamically tuned ring laser gyro. No moving parts. Settling time: 3 hours." No moving parts. That felt wrong to Saito. A ship without a spinning wheel of bronze and copper was like a heart without a beat. But the numbers were seductive. Accuracy: 0.01 degrees secant latitude. Mean time between failure: 50,000 hours.

The replacement was a Yokogawa CMZ 700. It arrived in a crate the color of a stormy sea, its interior packed with desiccant bags and the sharp smell of new electronics. The manual was a brick—three hundred pages of A5 paper, spiral-bound, with a cover as blue as a winter sky. it read in crisp sans-serif. Below: "OPERATION, MAINTENANCE, AND ALIGNMENT."

It was the most poetic thing Yokogawa had ever written. It read, in dry technical prose:

He read further. Chapter 6: A list of things that could confuse the laser ring: rapid acceleration, magnetic storms, nearby large masses of iron… and undersea geological anomalies .