The market is flooded by $10 Chinese angle guides. They all look the same. And they share the same problems: they damage sharpening stones and they are damaged by sharpening stones. And you cannot choose the angle.
Hapstone T1 Adjustable Angle Guide is different. You can set any desirable sharpening angle in a wide range (approximately 13°-30°), and the angle will be consistent during the sharpening on the sharpening stone. T1 Angle Guide slides on the surface of your working table and does not damage the sharpening stone.
T1 Angle Rod does not have a user's manual.