For me, I find the TNT to be 100%. If it slides its not set. If it digs in and feels consistently sticky and gritty I feel thats an indicator. I always do a visual to follow the striations which is like a pre test but i always verify with the TNT. Now gritty to me means consistent diggy feeling throughout the edge, no variation in the feel at all. Dont forget to do additional laps to return the edge o pre TNT. The test dulls somewhat.