you're not in valet mode by chance are you? But i agree with others. Video Record it
Can’t see how you can hope to be accurate with manual timing.
All of the variation is going to be with your manual process and not the car (or any car)
If accuracy is important - and as we are talking .1 of a second differences I’m assuming it is, then the only option is buying hardware to do the timing.
I can't believe OP is going to waste the time of a tech at the Tesla SC with "I try 0-60 runs with google maps and the accelerometer on my phone and don't get consistent results".
What. a. joke.
Yes, as others mentioned you don't need to look at GPS or distance data at all. That would be relevant if you were trying to emulate a 1/4 mile run but for 0-60, the best way to do it with a stopwatch (if you HAD to do it that way) would likely be:
Have a passenger holding a stopwatch. Have him "start" the moment he feels his body pressed into the seat (replace him for her if you have an awesome girlfriend). The slight delay in reaction time will closely match up with rollout (+/- 0.1 second I would imagine). Then stop the stopwatch just after you see 59mph on the display. That is likely more accurate than waiting for 60mph as there is some filtering on the speed displayed on the screen.
Alternatively you can do the exact same thing with a GoPro or other camera, as you can clearly see when the acceleration starts and you can see the speed displayed. So you can spend some time looking at the video to determine the exact start and stop point, not ask the passenger "are you sure you pressed stop just after 59mph showed up?"
Try that and compare your results, I'm sure you will find them closer to published numbers.
If only you speak less and read more, I've mentioned often that I'd be ordering / trying out more accurate device. I am even asking how others do. This is not a forum of "results" but questions, if you realize.
Most of us who do drive cars are certainly not in a full on profession to own acceleration test gear for the cars; let alone after buying a Tesla.
stomp the pedal literally, none of that hard press crap... warm the battery up prior to the test and get a proper measurement of the speed via go pro. test it forward and back on the same street 3 times... report backBattery was charged to 170 miles and not the full 310+ miles.
Nothing else odd or unusual.