"Does anyone know what the bench rest shooters use to measure their powder charges with? The guys that make one hole out of 5 shots.... If they use a digital scale what kind do they use??"
Many use the measure you mention. None I know of use digitals, NOT practicle for loading at the range the way they do.
Let me suggest you may be overly agonising checking/weighting powder. The BR guys don't, they know it's not neccessary. What allows them to get one hole groups is a LOT of things other than precise powder charges.
Cases are selected by weight and neck consistancy, then they get neck turning, primer pocket uniforming, flash hole uniforming. Loaded with precison, hand made bullets. Barrels are not only from precision makers but many have tried multipule barrels to get a "hummer". Sighting with very high power scopes, often selected again from several to find something that will hold zero, sitting in some pretty expensive solid rings and mounts (NOT Redfield, Weaver, Burris, etc.). Triggers are in the 2-4 oz. range. Hand-laid fiberglass stocks with actions epoxy glued in, stress free, not screwed in. Shot from heavy, precise front rests and specially filled and perfectly positioned rear bags, off concrete topped benches that are solid as a rock, while watching 3-5 windflags at different ranges.
Precise powder charges are perhaps the lest significant part of the total picture for shooting those tiny groups. In fact it's been demonstrated that a couple-three tenths powder spread means nothing over the short 100-200 yard ranges the BR crowds shoot.