On SS Maihar when I was 4th Eng. on 8-4 I used to have a competition with the 2nd and 5th on 4-8 to see who could use least fuel! As 4th I used to pump up the two settling tanks in the two wings above the engine room (a big space and formerly used to take crews back from Indian to UK for ships in UK, possibly coal bunkers in early days) which fed the boiler fuel pumps by directly by gravity, we had pneumecators only for these two tanks which was then used to measure consumption.
I used to fiddle with the feed heater water levels, slow the condenser circ. pump such as to maintain enough vacuum only, knock off one of the dinky steam driven elec. generators if load was low, (and warn the 3rd mate to let me know in plenty of time if he was switching on the radar and make sure I had a hammer ready to give the governor a gentle tap!) plus warn the Tindal to keep dead on 250 red line only on boiler press and generally play about with the steam pumps etc. I seem to recall that the average consumption per watch was about 9 tons using four Scotch boilers when steaming , could this be correct as memory is fading after 64 years!