OBC not accurate?

[Scarface]

Ever since I got my 325i, my OBC has always been off...Like when driving and starting to slow down I can check my speed and it is way off, but when I hit the reset button it seems right but not for long...Same goes for my gas mileage on there too...Well the other morning when I started the car it read "OBC not accurate see owners manual" or something along those lines...That may not be the exact phrase it said but it said to see the owners manual..Is there a way to fix it by reading the manual?

[KC Ron Carter]

You may want to read the part of the manual that explains the averaging between resets. Not a flame, just a note, that the OBC is operating normal.

Later,

[CyPHER]

The speed button is an average speed readout. The same goes with the consumption button. That would explain why it is not accurate.

[Scarface]

Ok that explains! I did not know that because I do not have a manual. I may need to look into getting one..Thanks for the help guys!