As you become familiar with your router the need for a device like this fades. Every router has it's own voice so to speak. The best tip for new users is to listen and see if the motor slows down or is laboring. This would show you are removing too much material in one pass for your router to handle. Another part of the voice is different sounds when routing like a skipping sound which is called chatter. This happens when the router is not cutting cleanly and could be caused by a dull bit or cutting against the wood grain. Listen when your router "speaks" to you.
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