HUD Not Accurate??

I have a 1998 GTP that I just recently installed a new, Pioneer head unit in. Because I had to disconnect all the wires and turn off the battery, the HUD ended up resetting. The only thing that's weird is that before the head unit was installed, the car was getting around 21 mpg according to the HUD, but now it won't even go over 17, it consistently says 16.6-16.8. Any ideas why?? It's not a big deal, just curious. Thanks!

You mean the digital info center?

Well, if you only drive city and or short trips from place to place getting 17ish is not abnormal.

Get some highway miles in and your average will be much more average.