Zbman what I meant was that I was making a guess, rather than the figures being guesswork.
Being an average, the contribution of the constituent bases and rotations is impossible to discern from the figure. I believe that there are some bases that shore this figure up through consistent punctuality, whilst many others drag it down.
You ask why I think it's pisspoor?
Because the schedule is unrealistic, that's why. You can make on time departure 90%+ assuming nothing too out of the ordinary. Much in the same vein as performance figures, the timetabling simply has to reflect the realities of the operation rather than an idealised model.