If you plan on sharpening knives, you should invest in a truing stone. If your stone’s dished up like a skateboard it becomes impossible to maintain a consistent angle, and you can't sharpen any more. That’s where the truing stone comes in to play. It is much easier to keep your stones flat than making them flat. We use a truing stone every few knives we sharpen.
This Truing stone is big. We turn our stones over and work them on this XL plate truing stone and it works magic. Rougher than the regular truing stone, this will ensure your coarse stones are flat for days when truing regularly.