What are these engine gauges in the Comet 4 for? What are these gauges on the Comet 4's engine-gauge panel (between the captain's and first officer's instruments, above the throttle levers), marked "POWER LOSS INDICATOR", for?  (Sorry for the blurry image.)



(Image cropped and annotated by me; original by Geni at Wikimedia Commons)

I'm assuming they're engine gauges of some sort, since there're four of them and they're located immediately below the engine RPM and EGT gauges (and above the throttle levers); could they be for monitoring engine performance during hot-and-high takeoffs?

They are apparently not present in the Comet 1, which instead has engine oil temperature/pressure gauges in this area (see pages 59-60 of this PDF, marked as pages 58-59).
They were used on takeoff to monitor engine performance. Takeoff power should result in the needles moving to the vertical marker and all engines should be registering the same reading.

The indicators monitor the pressure in the exhaust cone of each engine and will give a warning of failure which might in certain cases only become apparent by watching a combination of other instruments.