The flow of information needed for sure adaptation of PALs starts with Point of Booking the order and ends when wearer is happy to wear it. The order of steps being Pupil marking, centring the lens for edging, fitting it in the frame after edging and restoring the centring to the marked position.With wrap, tilt and nose pads. The error in each step amounts to creat deviation from Desired positioning. So,there are errors in series.In worst situation, the errors should build up to drive away the Centre of lens as far as possible. The PAL able to handle this maximum error with ease shall be sought after by all opticians. So, what one should love is the tolerant Pal and hate intolerant one..