Help, I need to buy a torque wrench

A bolt is like a spring. When you torque it, it stretches. If you over torque it it stretches past its (yield)limit to recover, now its useless. if you under torque it, you are not getting its spring clamping characteristic. When looking at a bolt being torqued, check its position at min and then check at max ratings. I bet its about 1/4 turn max. At 20 tpi, 1/4 turn is .0125 inches. .0063 is an ARP stretch value for a SBC rod, thats 1/8 turn variance. torque wrenches are pretty accurate considering what they do. You be the judge.