Why Your Trip Numbers Might Not Add Up

[Guardian_Bob]

So I was looking back at a picture I took a couple of weeks ago, Trip 2. I've left that counter alone since I've gotten the car.

 

It claims 927.2 miles @ 31.1 MPG consuming 29.72 gallons of gas.

 

Great, so I take 31.1 MPG and multiply by the number of gallons consumed (29.72) and I get 924.292 miles.

 

That doesn't add up, or so you might think.

 

If you take the gallons 29.72 and divide it by the number of miles 927.2, you get a MPG of 31.19785.

 

Rather than rounding, the computer is truncating after the first digit. This is likely true with all items. So what does this mean?

 

1. Distances, gallons and MPG are likely understated by less than one tenth (or hundredth as the case might be) of a mile (gallon, etc.) but are never overstated.
2. The computer is tracking more digits than it shows (otherwise this truncation would cause a much bigger difference than 0.3%).
3. I've got way too much free time on my hands.

GB

Edited June 24, 2013 by Guardian_Bob

[gadgetguy]

So I was looking back at a picture I took a couple of weeks ago, Trip 2. I've left that counter alone since I've gotten the car.

 

It claims 927.2 miles @ 31.1 MPG consuming 29.72 gallons of gas.

 

Great, so I take 31.1 MPG and multiply by the number of gallons consumed (29.72) and I get 924.292 miles.

 

That doesn't add up, or so you might think.

 

If you take the gallons 29.72 and divide it by the number of miles 927.2, you get a MPG of 31.19785.

 

Rather than rounding, the computer is truncating after the first digit. This is likely true with all items. So what does this mean?

 

1. Distances, gallons and MPG are likely understated by less than one tenth (or hundredth as the case might be) of a mile (gallon, etc.) but are never overstated.
2. The computer is tracking more digits than it shows (otherwise this truncation would cause a much bigger difference than 0.3%).
3. I've got way too much free time on my hands.

GB

 

That's very interesting and yes you do lol.... Thanks for the info!

[corncobs]

Yep they don't like to show rounded numbers!

It makes the MPG look better bad; your result is the perfect example; it makes tech savvy people scratch their heads that 31.19 is displayed as 31.1

I think the majority of people will never reverse engineer the numbers like we do so I guess we know the right way and can calculate the correct numbers.

 

Fixed my screwed up post! :doh:

Edited June 24, 2013 by corncobs

[Guardian_Bob]

Yep they don't like to show rounded numbers! Which can be a good a bad thing. On one hand it makes the MPG look better; your result is the perfect example; on the other it makes tech savy people scratch their heads.

 

I think the majority of people will never reverse engineer the numbers like we do so I guess we know the right way and can calculate the correct numbers.

?? Better? It makes the MPG look worse. 31.1 truncated vs 31.2 rounded.

[corncobs]

?? Better? It makes the MPG look worse. 31.1 truncated vs 31.2 rounded.

No I'm sorry you are right!!! what the hell was I thinking ???

[neod192]

Yup, the Fusion does this...