Real time MPG tech ?

Does anyone know the technology used for the real time MPG displays in newer cars..Is it vacuum driven sensor or fuel delivery sensor. Other!
Are there after-market add ons that are reasonably easy to install and cost effective?

Vacuum gage.
Used way back in 1970's before they had computers.
Also one of the oldest and cheapest engine testers

I used vacuum gages in the fifties and I am sure they are still useful today. I am trying to find out how the new digital readouts are driven. I have not seen any digital vacuum gages. I am not saying they don't exist for I don't know. It's just a curiosity to me.

I used vacuum gages in the fifties and I am sure they are still useful today. I am trying to find out how the new digital readouts are driven. I have not seen any digital vacuum gages. I am not saying they don't exist for I don't know. It's just a curiosity to me.
I would say some are tied into engine vacuum sensors someway
What year make and model and engine?

Well, My brother has a 2006 G Caravan that has a digital read out and I know other mfgs do as well. Make and model I don't think is relevant in the quest for understanding the tech used here. I see that Bullydog and other aftermarket tweakers offer this add on along with other functions but at a ridiculous cost (if all you want is real time mpg that is). Thanks for the input. I pretty much think it has to be driven by vacuum sensors but then I really don't know if there is is some other way. Just can't see the vacuum being that accurate a measure.

Well, My brother has a 2006 G Caravan that has a digital read out and I know other mfgs do as well. Make and model I don't think is relevant in the quest for understanding the tech used here. I see that Bullydog and other aftermarket tweakers offer this add on along with other functions but at a ridiculous cost (if all you want is real time mpg that is). Thanks for the input. I pretty much think it has to be driven by vacuum sensors but then I really don't know if there is is some other way. Just can't see the vacuum being that accurate a measure.
Make and model is very relevant for me.
I just like the parts man that asks for year make and model and engine and hoe many doors and what color and so on.
And then after you tell him he asks the same thing again a time or two.

If I had year make and model and engine I could look it up and see what makes them tick or if you would get some good repair info you can look it up in it.
Might be interesting to see for sure.