why is my bike odometer differ than a trail milage?

i was on a trail , complete way around the trail is marked 12 mile, i do the trail my odometer reads 19 miles, Why?

John M2013-06-06T07:54:50Z

Favorite Answer

You entered the wrong circumference number into the computer. Check it against a mile marker on the road or trail.

http://sheldonbrown.com/cyclecomputers/index.html

Edit:
Make sure that it is reading miles not km 12 miles = 19.35 km You change it during the set up.

silverbullet2013-06-06T13:18:28Z

Well, one or the other is wrong.

That large an error suggests your odometer is set wrong. More than likely, you have it set for km rather than miles. Consult the instruction sheet that came with it.

Mtrlpqbiker2013-06-06T19:30:27Z

Silverbullet and John M have hit the nail on head. Your computer is reading in kilometers, not miles

?2013-06-06T20:19:42Z

12 miles and 19 kilometres is the same distance. My guess is that your computer is set to kilometres/kph.

Cooper2013-06-06T16:11:21Z

Check the settings.