I've been reading with interest about the discrepencies you guys have been finding between different tensionometers as I went through quite an exercise in this last winter. I was experimenting with several sets of identical wheels all using Ambrosio Nemesis rims laced to Campy Record hubs with DT Swiss Comp and/or Revolution spokes. I have both a Park TM-1 and a digital DT Swiss Tensio gauge and was getting significantly different readings from both, the Park reading the higher of the two. My curiosity was getting the best of me so I sent both meters back to the manufacturers for calibration. DT Swiss said the tension was spot on and Park adjusted theirs a bit. Even after factory calibration the readings are still significantly different.
I have a spreadsheet I created which makes quick work of conversion of the readings which I've reproduced for one of my wheels which I purposely built up with a very high tension, perhaps too high. There are two charts, one created using the DT Swiss Tensionometer, and the lower one created using the Park TM-1. I'm curious to see if the Nemesis rims will hold up to this tension without cracking at the nipples, particularly on drive side spokes number 7 and 8. I should say that I increased the tension after riding for a while at a lower tension only to have a non-drive side spoke go slack, albeit on a different wheel (but same specs), built using the TM-1 which in retrospect was reading high and thus built up a wheel with less than optimal tension. So, while the Park tool is fine to get relative tensions, I rely on the DT Swiss Tensiometer for what I believe is a more absolute measure, particularly when using DT Spokes.
In summary, the Drive side tension reads an average of 130kgf using the DT Tensiometer, while the Park TM-1 gives me an absurd average tension of 157kgf for the same wheel using the most current charts from both DT Swiss and Park. The DT Tensiometer also can reproduce the results within .02mm of deflection. The Park is less reproducible but still does the job.
I think the optimal drive side tension for this build is in the 120-125kgf range. The above wheel may be a little on the tight side, but I like experimenting, even if it means wrecking something here and there along the way to determine the true limits.