This sounds strange; I have an HB 917 (2006) on a separate antenna; when I long-line, I usually go about .6-.9 MPH--and it reads fine. No doughnut, speed seems to read fine. I've got a 997 on the console, no update, but I've never taken a look--course, I'm generally goin' in a relatively straight line with broad curves and turns, rather than the tight, back and forth stuff I've seen some riggers do. I'd think I'll be able to go even slower and still read with a 4X refresh rate.