What you see with the Trip B selected is the instant mpg. Only Trip A shows the average miles per gallon. I initially had that question with myself but figured it out. When you reset Trip A the average mpg meter switches to what ever the display is after that. Then you have to select average mpg again and even then it takes more than .5 miles to show up. Every time you reset the trip meters the instant mpg (if that is what you have selected) reverts to the next display in the rotation. But the main thing is if you want to always show average mpg you need to have Trip A selected. If you want to see long term consumption you will have to leave Trip A alone for the duration of time you want to watch. BTW- Both trip meters only go up to 999 miles and then they flip over to 000.
As a side note. If you want more accurate mpg tracking per tank you will have to record the Trip meter mile for that tank and calculate the gallons used to fill the tank. Must start with a full tank.
If you want more accurate mpg tracking over the longer term, IOW several tanks of gas, you will need to record the main odometer and add up all the gallons used over the time you want to track and use those numbers to calculate the mpg over that range of time. This is because the mpg meter is WAY offset from reality. It is also very inconsistent. I've seen it show ave. 63 mpg for a tank but then I'll calculate ave. 59 mpg. Then another time it will show ave. 67 mpg and I calculate ave. 56 mpg. And still another time it will show 72 mpg ave. and I will calculate 60 mpg ave.
And even that is not totally accurate. In the same way that my speedometer is about 5.5% offset from actual speed (speedo shows just under 69 mph when my actual speed is 65 mph), the odometer is also offset but not by as much. Maybe closer to 3-4% offset so for every 100 miles I actually travel the odometer indicates I've gone 103 or 104 miles. I haven't nailed that one down yet but I have verified the speedo offset by using a GPS unit (.3% offset at worse) and also by measuring the time to pass mile markers on the highway at 60 mph until I was consistently riding for one minute per mile marker over several miles.
All of the above applies regardless if you have the meters set for miles or km, or have the fuel usage set to gallons or Liters. The operation and offsets still apply. I have found that different bikes of the very same brand/model will vary on how much offset there is. But all bikes will show slower than actual on the speedo. Legal and insurance regulations and such.
