Secret MUST item for using hard natural stones. Nagura stones cannot be used for harder natural stones, nor on various Suita stones.

The polishing parcticles of Nagura is larger than the particles of super fine finishing stones, and when the stone is hard, the Nagura's particle will scratch the bevel before they are ground to smaller size. Using diamond stone to create the initial slurry, you are getting the slurry that is made of the finishing stone itself. You'd be surprised how much better result you get by this technique.

Also, when you use a Nagura on Suita stones, the coarse Nagura particles will get stuck in the Su (the holes in Suita stones) and will keep scratching the bevel, because these particles won't get ground to smaller sizes.

Atoma is my most recommended diamond sharpener, since they are quite accurately flat (other diamond stones are sometimes not so flat, therefore will make the stone convexed or concaved when flattened using them) and also the price is cheaper than other equivalent quality diamond sharpeners.

#140 11000
#400 10000
#600 10000
#1200 10000

I have tested other brands in and out of Japan which are below $200 range, and Atoma was siginificantly better in quality than the others in my opinion. The marks are much finer and even, the glide is smoother. Only more expenisve ones that are over $200 would compare in quality.