If you have a surface planer that uses double edged knives, you probably have the same trouble I did… remembering if you'd already flipped the knives over or not. Here is a trick I worked out to help me.

If your planer knives have a brand name or emblem stamped on them, just make it a personal policy to ALWAYS install a new set of knives with that emblem in a particular position. On my Delta planer knives there is a triple triangle emblem, I install new knives with that emblem "pointing" out toward me. If I pull a set of knives off the planer and the wide end is pointing out toward me I know that this set is used up and I need to install a new one.

If you are absent minded (like me) it pays to tape a little chart to the motor housing to remind myself what the policy is.