How accurate does a torque wrench have to be?

I will do the test a few more times to make sure that I was accurate. I didn't see a calibrations sticker on my 1/2 drive wrench, but there was one on my 3/8 drive wrench, it was from 99 though lol, tested it the same way and it seemed even more accurate than the other one. But if some don't use click or beam wrenches for assembling parts what do they use?

And that's the margin of error with my measurements, I knew the weight of the water in the bucket because I measured it and used that to convert it into the total weight including the bucket, I also weighed it on a scale (not overly accurate I don't think), but because it was pretty full I spilt some, and there are slight variations when I measured the water as well as the location of the weight on the wrench handle.

So to add how accurate are beam wrenches? Because I like the idea of torquing with a click type and confirming that the torque is correct.