Automatically sync chart speed with boat speed?

That dude looks just like me, wait it is me :)

Would rather see chart speeds less than 1 available for slow/drift fishing. GPS speeds are not accurate below 1 or 2 MPH and tend to jump around a lot.....

Could somebody give a idea of how to match it. I try to match the hb with boat speed but always that uncertainty. Ex. Hb 2 boat .7 hb Ultra boat 25.. just put them numbers not really accurate

1mph chart1, 5mph chart5, etc... Don't expect ultra/10 to work at plane unless you have a high speed setup. SI at wot, forget about it.

So what's the fastest boat speed you would operate at with each type of sonar . 2d di and si