How accurate is the mpg indication on my Honda?

There is a discrepancy between the miles per gallon achieved as indicated on my Honda's display and the figure I get by carefully checking miles on the odometer divided by the declared amount of fuel delivered, taken from one brimful to the next. The latter is always 7 per cent less. Either the car does not accurately compute the correct value or the pumps are showing an optimistic amount. How often are the latter checked?

Asked on 12 January 2013 by RW, via email

Answered by Honest John
It's the same with most cars. My BMW shows 70 when I'm really getting 65 (I'm not complaining).
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