Measuring tension in double butted spokes I'm building a wheel with double butted spokes, 2.0 mm at the ends, 1.8 mm in the center. The Park Tool Spoke Tension Meter has a conversion sheet to determine the tension in spokes of different diameters. My question is which scale to use: 2.0 mm or 1.8 mm.

Logically, I think that I should use the 1.8 conversion, because the center of the spoke is 1.8 mm diameter. But the entire length of the measured section is probably not 1.8 mm, because it is tapering to 2.0 mm at the ends.

The answer to this question suggests there is some acceptable variation, so I was thinking about aiming for somewhere in between.
Tensiometers test deflection and their charts make the assumption that the entire section being used for the test (the entire length of spoke between the tool's two contact points) is a uniform thickness. That way that section is isolated - if there were any of the taper in there, it would throw off the reading. So you always make sure the tool is touching only the thin section, and you use the chart entry for the thin section.