Someone,somewhere in some office ,probably came out with the statement;"we'll do it in 9 days".
I once worked for an airline,where someone in some office,somewhere,had done some research and came up with figures for each route and load that amount of potable water on to the b747.Great said the management this is going to save us pennies.
Anyway I,m sure you've all guessed already,that the first flight to Vancouver ran out of H2O en route,hence urgent telex issued to disregard those figures and fill em up.Never did hear what happened to that guy?
Those 9 day c checks can be done if the aircraft has been exceptionally well maintained and you put blinkers on so you only do exactly what is on the job card!