<VV> Discrepancies with main odo vs trip odo

[Rick Loving]

My 66 Turbo started its life as a 66 Monza and currently has the parts
from a 65 Corsa (engine/trans 180/4speed with 3:89 diff) 
 
The car currently has 215/60R15 tires which are around 25.14 inches in
diameter, I had my wife pace me and 60 mph in out minivan equals 60 mph
on the vair speedo.
 
The car has a Corsa dash with the trip odometer as well as the main
odometer, but they don't seem to match up.  I have been tracking mileage
and noticed that the numbers on my main odometer don't equal the miles
totaled on the trip odometer when I compare them.  I thought it might be
my math from start so I just used the most recent numbers.the trip
odometer is reset at every fill-up...
 
Odometer reading 
Main     Trip
Start     end
5974
6108     144
6230     130.2
6277     50.8
6434     168.4
 
If you use the main odo and subtract the previous mileage you come up
with
 
134 instead of 144
122 instead of 130.2
47  instead of 50.8
157 instead of 168.4
 
The trip odometer is reading about 7% higher for every mile driven,
when I watch the main and trip odometers the main appears to change
different on every rev of the trip.
 
Anyone have any idea's why these don't equal each other and which should
I trust when calculating my mileage?
 
I am perplexed as to why they would be different.as I thought they would
both read from the same source.
 
Rick Loving