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The Sinus Zero Line was the first putt and approach golf disc released by the Swedish company Latitude 64. The Sinus has a very flat top with textured grip pads for your thumb. The Sinus is slightly over-stable, allowing it to be thrown hard on longer putts/approach shots without losing consistency. This Medium edition really lets you feel the disc's shape and adds grip in warmer climates.
The Zeroline Medium plastic really is the happy medium between Soft and Hard Zeroline. It has a firm feel with plenty of grip mixed right in.