I loosened all the adjustment screws and then primed my oil system before doing anything else, so, in theory, the lifters would be pumped up and I could accurately set my lash.
I don't have adjustable rockers, but I imagine with hydraulic lifters if you loosen the adjustment screws then prime the oil system none of the lifters would get pumped up.
My brain ain't braining, someone learn me on this please.