Green reading is feel based IMO as a lot of how a putt will move is directly related to speed. The secret is to start with a solid foundation of the lay of the land. All greens MUST drain – there is always a low spot (or many) where water will move off the green. When standing on the surface, sometime you can feel the subtleties in your feet – but if you seek out the drains surrounding the greens, this will give you a general sense of where the water…and hence, the ball…is moving. This too applies to mountains nearby (breaking away from), valleys (breaking towards), and even the setting sun (affects grain). Understand these fundamental principals and you will more accurately read more putts!