Do you point the arrow in the v-groove or on top in between the grooves? Also while I've got you can you get the same razor sharp edge with the new sb 250 Blackstone that I can with the sg-250. I have some Doug Thompson tools I am sharpening and the sg-250 is fine but it is barely in the water. Nearly time for a new wheel. Thanks Jeff.
Jimmy,
It doesn't matter whether you reference to the peak or the groove. It only matters that you do it the same way every time. Personally, it is easier for me to see alignment to the peak.
If your focus is on turning tools, I would recommend the SB-250. It delivers the same finish, but has better wear characteristics and cuts faster. However, if you work in both HSS and normal carbon steel (bench planes, chisels, knives, scissors, etc.) and only want one stone, then I would stick with the SG-250. You might consider getting the SB-250 now, before your SG-250 is completely worn out. Then you could use your old stone when sharpening carbon steel.