People who are not overly familiar with sharpening knives on a whetstone might find this little tool useful:

It slides on the spine of your knife and ensures a consistent grinding angle being maintained easily.

This one is made from a 120 mm piece of electrical tubing with a 20 mm diameter. The slit is ~1.5 mm wide (see drawing). You can easily adjust the grinding angle to your personal needs by just using different sizes/diameters of tubing. It’s done in five minutes, it doesn’t cost a dime and it’s really useful.