A mechanical watch needs to be "recharged" to regain optimal performance. A fully wound watch gradually loses its torque after some time, and this may also result in loss of time-keeping accuracy.
How does one maintain a steady rate of power delivery, and thus accuracy? There has been a number of solutions, one of them being the constant-force escapement. We've already seen this in Swiss watches like Girard-Perregaux, but this innovation appears for the first time in a Grand Seiko—specifically the Grand Seiko Kodo Constant-Force Tourbillon.
See also: Japanese Watches With Hidden Superpower