It doesn't have one (the SL95, AP76, SL72B, etc. I can't remember the general inner null point for the Zero. Should be ok at 1.25g with bias set to 1g or less if mine's anything to go by, but watch warped records for excessive 'wobble.' I don't know the dynamics, but the cartridge is set well below the plane of the bearings and tonearm - not sure if this has an effect on warp stability as I don't think the arm is *that* massive? Look after the 91-ED if it's a Shure original stylus (yellow stylus housing and Hi-Track printed in red? on the front). I can't remember the general inner null point for the Zero and related-length Garrard arms of this era, but if you line up as above and then check with a card type protractor, it should give perfect alignment at either 60mm or 65mm approx. I'm in trouble on the Dual forum as regards cartridge alignment, but A70BBen's advice above should be all you realistically need as the arm will do the rest. I've used my V15 IV in the Zero with no difficulties whatsoever :D If you like the V15 IV's slightly understated tones (NOT a criticism as I like mine too), the Zero 100 arm will happily track it as it has the excellent damper to minimise the effects of tonearm mass and by inference, you'll LOVE the97XE too on this deck.
#Garrard zero 100 s for free
EVERYTHING from the speed change mechanism to the start-stop lever under the platter will need doing including checking the cam parts for free dry movement (the 'operating' groove in the cam may have a black tar like substance there already and this should be left as-is I think) and to fully refine the nice clean mechanism, an O ring on the bottom of the geared part of the platter hub (13mm x 1.6mm I think or slightly larger in overall diameter as long as it doesn't fall off) to quieten it down when cycling - amazing what this little part can do, but most/all later Garrards of this type had this to increase perceived refinement and it works a charm. Obviously, the deck will need a bloomin' good seeing to, so the greases all over can be removed and sparingly replaced with a longer lived equivalent. I say this as I suspect the Pickering you have may be underselling the deck a bit.
I use an old Ortofon VMS10E II in mine to good effect and I think a 510mk2 and 520mk2 or Shure 97XE would be good as well if you can find a good used one. The arm isn't the most rigid and the added bearings add some slop to the proceedings. These are rapidly appreciating conversation and collectable pieces now, so whatever the sonic qualities, it's well worth carefully restoring the machine and getting it working right :D