My employers had seceral ETP students flying with us as " U/T F/Os" to see what Ordinary flying was like, with average crews, ie. not all of us perfect ! ( I just hope that I was not used as " the bad example.")
Some years later I was appointed the " Fuel Economist" for the FOUR fleets who naturally used four different ways of showing their crews the cost of fuel , then rapidly increasing. ( Old pennies per gallon, percentage of home base cost and two others better now forgotten.) Each fleet knew that they had the only proper way.
No one fleet could be favoured. A NEW way was imposed ( by the Fuel Economist ) listing fuel as £20/ tonne for example. To preserve commercial secrecy a small fudge factor was applied so that anyone else would not know. Purists might haggle that S.G. should be applied too !
LT