A fruit machine had been installed in the bar. This could be adjusted to retain various percentages of money put in and was therfore set to maximise payout.
A similar machine was installed in the College Hall Officers Mess at RAFC during my Graduate Entry time. One of the student Mess Committee members (all officers in those days, of course) was required to ensure that it was emptied periodically and that the proceeds were sent to NonPAs or wherever - somewhere in Blunty land.
It too had a variable payout control. So, before leaving for work each morning, the student Mess Committee member would turn the payout control down to its minimum setting. Of course the permanent staff and others who frequented the bar at lunchtime would have little luck with the thing. Then, during 'Nelson's Hour' when the bar was shut for the bar staff's evening break, he'd turn the payout control up to maximum - so we students could subsequently reap the benefits of the ground pounders' lunchtime sessions.
They never did find out.....