A while back I seem to remember someone mentioning that Bob favoured the Stevenson. There are a lot of misconceptions surrounding the Graham jig. For example there is a popular belief that the graticule window weight corresponds to average downforce e.g. 1.8g. If this were true Bob would be inundated with complaints from those whose carts require lighter forces. Effectively it would destroy the suspensions on some of those carts, long term.
The reality is that the window only weighs approx. 0.5g (as stated by Graham distributor). The disadvantage of this is that it will necessarily incur a smaller deflection of the cantilever (less compression of the suspension than normal). This would cause an error but...as if in a self-compensatory manner, the angle of the window is never horizontal and will tend to offset this error.
Before users begin to "freak out" the size of the resultant error is probably less than 1/3rd the diam of a human hair i.e. not the sort of thing that even the steadiest hand will rectify without making it worse (this assuming the cart dimensions are even as claimed!). Also, the jig itself has tolerances otherwise it would seize :) These tolerances may also work towards reducing this error rather than making it worse(?)
Typically, headshells that use the 3-point mounting system will be worse than this and won't have the capacity to offset angle for badly oriented cantilevers - they have to accept the cartridge condition, warts and all...
There are a lot of unknowns here so the best advice is to do your best with the alignment and be happy. :)
I genuinely hope this helps rather than upsets :)
