"Bad torque follows rotor"
A previous Chief Pilot (and excellent instructor) taught me this to help navigate the situation that Nick mentioned above; differentiating from a high-side vs a low-side gov/fuel issue in a twin, specifically a B212/412 with a dual torque gauge. During a failure, the torque needles will split, one increasing, the other decreasing...how do you know which is the affected system?
If Rotor is increasing and your TQ is split with Eng 1 TQ increasing then you have a high-side failure on Eng 1.
If Rotor is drooping, and Eng 2 TQ is decreasing, you have low-side (or failure) on Eng 2.
Bad torque follows rotor.