A. Neutral buoyancy: computed vs simulated
Closed-form ballast mass for neutral buoyancy at a depth, then the simulation is run three ways: hold, release with a small mass error, and terminal sinking speed.
B. PID gain sweep: oscillation vs damping
Compensating-tank depth loop, 2 m step, Kp from the slider, derivative gain swept from 0 to 2x critical. Measured period is compared with the root of the linearised loop (cubic characteristic polynomial).