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Hi guys! Thought I'd pass this along here, it's an app called AniRef for iPhones, iPads and iPods.... It lets you record or import reference, track arcs, frame by frame, bookmark key poses and play footage in slow motion aside from other stuff...

Their site is www.aniref.com
https://itunes.apple.com/us/app/aniref/id897387321?mt=8
Hope it helps! :)