Steeling helps maintain sharpness. This process realigns the edge, correcting for dulling causes such as a rolled edge. A sharpening steel is a type of hardened cylindrical rod used similarly to honing stones. For example, a butcher steel is a round file with the teeth running the long way, while a packer steel (used in the meat packer's industry) is a smooth, polished steel rod designed for straightening the turned edge of a knife,[7] and is also useful for burnishing a newly finished edge. Because steels have a small diameter they exert high local pressure, and therefore affect the knife metal when used with very little force. They are intended for mild steel knives that are steeled several times a day, but are not well suited for today's tougher and harder blade steels. Diamond steels are now available that have an industrial diamond coating and can remove blade metal as well as straighten, therefore used correctly they can re-profile a knife instead of just honing. 

But it's a different type of sharp, according to Joe Authbert, product development manager at ProCook. "What it does is add tiny little micro-serrations onto the edge of the blade." But fear not - your smart knife won't end up looking like a bread knife, as you'll be hard-pressed to spot the serrations. "If you looked at it under a microscope, on the cutting edge, there are these little lines that generate the sharpness, rather than a waterstone which is a smooth sharp edge," says Authbert. 

I've only used it to touch up the edge on an ESEE RB3 and a pocket folder so far, but it has done very nicely for those tasks. I found that using the rounded edge works best for me in order to be able to run the length of the blade without hitting the leather lanyard. I'll hopefully try it out soon on fish hooks, too. A worthy and handy accessory, and cool looking necklace, to boot!

The smaller the angle between the blade and stone, the sharper the knife will be, but the less side force is needed to bend the edge over or chip it off. The angle between the blade and the stone is the edge angle – the angle from the vertical to one of the knife edges, and equals the angle at which the blade is held. The total angle from one side to the other is called the included angle – on a symmetric double-ground edge (a wedge shape), the angle from one edge to the other is thus twice the edge angle. Typical edge angles are about 20° (making the included angle 40° on a double-ground edge).[1] The edge angle for very sharp knives can be as little as 10 degrees (for a 20° included angle). Knives that require a tough edge (such as those that chop) may sharpen at 25° or more.
Oil stones have been around a long time, and while not as popular as in the past, they are still a practical option. Not as fast as the other stones, they are easy to use and their lower price makes them a good value for the budget conscious. With oil stones, the relation of the types and grits can be confusing. Our article, Difference in Sharpening Stone Materials, provides a more in depth explanation, but in general an India stone or two combined with an Arkansas stone is a good combination to start with.
4. Start sharpening the first side of the blade. With your blade set at the prefect angle, you’re ready to start sharpening. Imagine you’re carving off a slim piece of the stone’s surface. Personally, I bring the blade into the stone. Other people stroke the blade away from the stone. Both ways work, so just use whatever technique you prefer. If the knife blade is curved or if it’s longer than the stone, you’ll need to sweep the blade sideways as you work, so the entire edge is sharpened evenly. Apply moderate pressure as you sharpen. No need to bear down hard on the blade. After you make one stroke, start back at the beginning and repeat. Do this about 6-12 times.
Diamond plates are available in various plate sizes (from credit card to bench plate size) and grades of grit. A coarser grit is used to remove larger amounts of metal more rapidly, such as when forming an edge or restoring a damaged edge. A finer grit is used to remove the scratches of larger grits and to refine an edge. There are two-sided plates with each side coated with a different grit.[14]