To check your speedometer for accuracy, you can use the following guide from Dakota Digital .
Seconds between mile marker = vehicle speed
Seconds = MPH
65 55.4
64 56.3
63 57.1
62 58.1
61 59.0
60 60.0
59 61.0
58 62.1
57 63.2
56 64.3
55 65.5
54 66.7
53 67.9
52 69.2
51 70.6
50 72.0
