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Easiest solution seems to be tweeting at Elon to get them to add it to the cars software
Seriously though, nothing cheap/easy is going to be very accurate. You can use a phone app that uses your phones GPS, but that's not going to be super accurate (+/- .2s?)
1) Get a dragy, as @Zoomit recommended. I own one and it works great with my Iphone 7.
2) Get the Stats app (Stats: For Tesla Model S/X/3). I haven't tried this one, just recently learned about it and it has great reviews. Apparently it can measure 0-60 using data directly from your car. A lot less money than a dragy, $10 vs. $150 - wish I'd known about it sooner.
...Sats app (Stats: For Tesla Model S/X/3). I haven't tried this one, just recently learned about it and it has great reviews. Apparently it can measure 0-60 using data directly from your car...
I don't think the Stats app will pull performance run data from the P3D. Tesla removed this functionality from all 3s before the 3 AWD was released, maybe removing from the late Spring manufactured (MCU2) S and X as well.
Would love to be wrong on this. We have sample data from over 200 previous runs, mostly from iOS PowerTools and Android Dashboard for Tesla.
The M3OC guys are pulling CANBus data directly from the 3, but they are still months away from deciphering the codes in the apps. Also you have to buy a CANBus dongle, take apart your rear console and (until someone sources the connectors) insert wires into the wiring harness. Probably doesn't meet your "simple" requirement, but accurate to a hundredth of a second.
That's the one. It has a magnetic base, so will work great on your metal rear package shelf. I centered mine under the rear window, as far back is it would go.