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How do I check my speedometer to see if it’s accurate?

You can estimate your vehicle's speed by measuring the time it takes to travel one mile. The best way to conduct the test is to set your cruise at one speed and time how long it takes to travel between two green "milemarkers" that can be found along interstates and other US/state highways.

Seconds Miles Per Hour
45.5 79
46 78
46.7 77
47 76
48 75
48.5 74
49 73
50 72
50.5 71
51.5 70
52 69
53 68
53.5 67
54.4 66
55 65
56 64
57 63
58 62
59 61
60 60
61 59
62 58
63 57
64 56
65.5 55
66.5 54
68 63
69 52

(Revised 07-2003)