Special tools are used that can measure the degrees a wrench or bolt has been turned, these are low cost protractors that has a movable pointer, whilst some tools use electronics when measuring a turning angle these can cost several hundred dollars. These two types both work well and though the electronic one is more expensive it actually can make the job go faster.

Some may ask the question why are the torque to yield bolts needed now? When perhaps they weren't needed in the 1960's or 70's. The answer to that question is quite simple in that engine materials are different now. For example, the aluminum cylinder heads expand differently to cast iron blocks. When an engine warms up, all the parts bolted together have to be able to slide on their gaskets or move against each other. Because of the elasticity in the torque to yield bolts allows movement between the parts but still maintains even sealing and clamping loads.

Engine parts today are a lot lighter than decades ago, the heavy cast iron parts was able to take variations in torque without failing. Aluminum alloys and thin wall castings that are used today need accurate torque if this is incorrect then leaks or warping can occur.

Today the design of engines is changing due to the need of even clamping forces, the car manufacturer Ford have prototype engines where bolts which hold the cylinder head on can go all through the engine block threading into the bottom casting which holds the crankshaft. It's hard to imagine that only a few bolts can hold a complete engine together. This would definitely change the way engines where assembled and disassembled in the future.The news come from http://www.bossgoo.com/