The crewroom for ship's flight was an old WW2 wooden shack with a coal burning pillar-box stove to provide some much needed heat in winter. Working on piston engines with petrol dripping down your hands and arms was apt to get a bit chilly, especially out on the hard-standing with the wind, and often rain, whipping around you. To the extent that at times it could take quite a few moments to put down one spanner in order to pick up the next.
There was seldom any actual coal for the burner but usually Jack could find flammable alternatives, wood, oily rags, yesterday's newspaper... Pusser provided plenty of rag for working on aero engines and airframe components, and it was found by trial and error that oily rags were probably the best fuel and that by judicious use of the flap of the ash clearance port at the bottom of the pillar-box and the flap of the fuel re-filling port at the top to regulate airflow, with oily or aviation turbine fuel (AVTur) soaked rags quite a lot of heat could be generated.
Once we had this stove going properly and the flaps set to maximum efficiency, the stove-pipe 'funnel' of the stove would start to glow red... Starting at the cast iron fitting for the smoke stack some joker had chalked rings about every two inches (Remember those ? Inches ?) going up this pipe marked off as a 'Temperature Gauge', indicated by the height that the red glow reached.
These rings were labelled thus: -
Warm, Warmer, Nice, Hot, Red Hot, White Hot, Shit Hot, Clear the Crewroom !