Pretty sure everyone uses true wind speed. Even if you don't have instruments you can probably estimate. I remember reading an article on polars in Sailing World (June 10, 2008) by Stan Honey and Jim Teeters that says, "
Most sailors can guess TWS within a knot."
Somewhere (
maybe this) I read the Loos PT-2 calibration is 38/1300 lbs (
Loos Table 1 seems to support this). Setting the shrouds to that tension initially may help you get more consistent 'turns to tune'.
