Some of the self-appointed tool testers on YouTube bought torque wrench testers, at least one was from SnapOn and it cost more than $2K. They say they cycled the torque wrenches 1000 times, but it's three times at each setting. I had my SnapOn wrench tested on their tester in a dealer's truck and found that it's 5% off@100 ft-lb.If you want to have some fun cut a 3" length off the end of a 3/4" allan key
Arm yourself with 2 x 3/4 impact sockets then go to your favourite tool supplier grab 2 tension wrenches set them to the same spec slip on the sockets then work them against each other . You will be lucky to find 2 that are within 10% of each other .
Jus like idiots who post their coil resistance was 22.3251 Ω because they have no idea about electricity . Ignorant clowns think because the tension wrench can be set to 224.5 in lbs it must be so much more accurate that the coarse scales on a deflecting beam.
Torques are only an approximation and the real number depends upon the slop in the fasteners, the materials, the presence / absence of lubricants and of course the weather & the temperature of the fastener and what it is holding together and of course the type of thread & the pitch of the thread & dimeter of the fastener and the surface area under the fastener, the size of the washers and a whole host of variables that have not come to mind at the moment .
Bolt hardness, intended or work-hardened, makes a big difference, too. I looked at the head bolts and they appear to be Grade 3 and because these need 140-180 in-lb (according to their data sheet) the head bolts are likely soft enough that the expansion of the head & block needs them to be relatively soft, so they can elongate. OTOH, the thread goes deep into the block, so any expansion is in a short region near the mating surface.
I bought a torque adapter, but checked out the Ikon wrench- the barrel turns much more smoothly but I really didn't want to drop $120 for something I won't use often. I was looking on ebay, FB marketplace, rummage sales, etc for a used one but then, can I really be sure it wasn't dropped/abused? When it comes to tools that need to be precise, I don't assume anything other than "if it's so cheap, it can't be very good".