On Thu, 20 Jul 2017 19:56:12 -0600,
rbowman wrote:

If mom and pop are not taking advantage of readily available data from
the on-board computer systems they are either driving a 1972 Old Cutlass
or they are not part of the conversation. This is 2017, not 1917 when
you measured the tank level with a stick.

What's the accuracy & repeatability of the dashboard reading you speak of?

As you must already know, the tach isn't all that accurate on today's cars.
The temperate gauge isn't accurate on current cars either.
Neither is the speedometer (to a few percent).
Nor the fuel gauge.

Why would a purely informational dashboard mpg display be accurate?
Or repeatable?

Maybe it is - but there's no reason for it to be accurate to +/- 2% of the
indicated reading. Even the $360,000 EPA tool, as I recall, wasn't accurate
to any better than that.

What's the accuracy & repeatability of the dashboard reading you speak of?