1987 GMC S15 Belt tensioner

You must be using a beam-type torque wrench. Those are accurate enough for what you're doing but they are hard to read. Mechanics use click-type torque wrenches. You dial those up to what you want, then it clicks when you get there.

Mechanics don't use torque wrenches on things like tensioner pulleys. That takes too long when they charge according to time spent on the job. We use common sense, but that can't be taught. If you're using a 3/8" ratchet or breaker bar, you probably aren't going to over-tighten the bolt. You can with a 1/2" ratchet. If he bolt is going into an aluminum bracket, use less torque than normal because the threads can be pulled out easily.