Judging 45 miles per hour is a lot different (and difficult) than knowing how far three feet is. I think the device is used partly as education, partly as a me

Judging 45 miles per hour is a lot different (and difficult) than knowing how far three feet is. I think the device is used partly as education, partly as a method for capturing the exact distance. It's less about "how far is three feet?" and more "I have proof you were closer than three feet".