Most of my fishing comes via spider rigging. I know speed has to vary some depending on the elements and fish patterns but my problem is determining how fast I am actually moving. As many on here say, .03 - .08 mph can be good speeds when rigging but if you do not have a high end depth finder to tell you that, what is the best device to pin point that slow of a speed? The little GPS app I have on my phone will do MPH, but nothing under 1 mph. I know there are many times that I am probably moving too fast/too slow but really have no way of knowing. Any help would be greatly appreciated.