Always 1.7 off…sounds like a conversion type error, going from knots to m/s or mph. At first I thought it might be an average problem, but since WD is reading higher than the max that doesn’t make sense. What version/build of WD are you running?
Only thing I can see is that your using different measurements on your site. Your dailylog appears to be showing knots, and your website is showing kmh. Part of your site, Dettaglio dati giornalieri, is showing even larger numbers and I’m not certain what scale is being used as it doesn’t show units. Best bet would be to see if Brian has any ideas, sorry I couldn’t help.