Bill, I have a 98 Catalina 34 with a ST50 Plus Wind that this year has been giving erratic readings. In true wind speeds of 10-12 knots it is reading 4-6 knots. I have reviewed the manual and I know I can correct for apparent wind angle, but I don't see a way to correct for wind speed. The wind cups seem to be spinning at the correct speed as others in my marina but my true and apparent speed is too low. Is this a situation I can correct or does the masthead unit have to go back to you folks for a recalibration? I have checked that it is reading in Knots/hr rather than meters or kilometers per hour.