If you happen to be a perfectionist, wheel building is not for you. You'll never get perfectly uniform spoke tension and perfect roundness, so the best you can hope for is close enough on both measures. Adding quantitative measurements can either improve your wheel building by providing additional feedback, or drive you to madness with the pursuit of perfect numbers. I use a tensiometer and that's been 90 percent positive. Today I build my first wheel with the aid of lateral and radial truing gauges from Morningstar tools. We'll see if this is a good thing.
I will say that the experience thus far has been good. The tools shipped quickly from California, and they included a handwritten note from the owner, Paul. That's awesome, right? Gauges now mounted to my TS-2, I'm diving in...
Update: first build--Powertap G3, 38 mm wide carbon clincher, Sapim CX-Ray spokes--is done. These gauges are very useful and well worth the $120. The accompanying instructions could be clearer, but soon enough you'll figure out the logic of the setup.
One trip around the dial equals 0.1" and each unit is 0.001". The wheel I just completed indicates a tolerance of +/- 0.005". This thing is fucking brilliant. (I can't say the same about building with CX-Ray spokes. More about spokes in the subsequent posting.)
Update two: this setup may be too accurate. I can now detect flat spots on the rim that are due to manufacturing defects. The current rim has 3 and they're about 0.002". Doesn't sound like much, and it's probably not, but it's annoying knowing they are there.