I guarantee a low battery has both a natural reduction in performance due to the batteries themselves and also an intentional reduction in performance by Tesla to stave off range anxiety. If your battery is cold, or has a yellow dashed line anywhere on the power gauge you can bet your performance is limited.
In terms of speed clocking, you don't need to stop the speed clocking yourself if you're using a specific speed clocking scenario that isn't data collection. If you want to time your 0-60 times then select the 0-60 scenario in the bottom slider of the Speed Clocking screen, then press the green start button for it to turn yellow waiting for you to reach the starting condition (0 mph for 0-60 for example). Once reached, the button turns blue and you're free to punch it at which point the button turns red. Once your scenario conditions have been met the recording will automatically stop. If you're using the data collection scenario, you will have to stop the recording yourself by pressing the red button.
You can then analyze the recording data within the app pressing the Details button where you're given raw numbers, calculations and an interactive graph, you can also export the graph image as-is or the raw data of the recording in CSV format right from the details dialog. You can also view past recordings if you chose to download the raw data to CSV.
I have a Model S 60D I recently upgraded to 75D, I then had it uncorked for an extra 1.0s off my 0-60 and verified it via speed clocking. Interesting to note, the uncorking raised the max power available from 275 kW to ~337 kW which explains the faster 0-60 times!
I recommend doing multiple recordings then averaging the results you find because internet connectivity between your vehicle, Tesla's servers, and your device can all play a factor in the accuracy of a recording.
Here is the uncorked sample:
Code:
Timestamp Speed Odometer StateOfCharge Elevation Heading Latitude Longitude Power ShiftState Range
1511810020741 0 14013.9 82 609 89 47.686165 -117.239008 2 D 156
1511810020991 2 14013.9 82 609 89 47.686166 -117.239005 40 D 156
1511810021241 5 14013.9 82 609 89 47.686166 -117.239003 70 D 156
1511810021491 10 14013.9 82 609 89 47.686166 -117.238997 112 D 156
1511810021741 14 14013.9 82 609 89 47.686166 -117.238984 139 D 156
1511810021991 18 14013.9 82 609 89 47.686167 -117.238966 177 D 156
1511810022241 22 14013.9 82 609 90 47.686167 -117.238941 204 D 156
1511810022491 27 14013.9 82 609 90 47.686167 -117.238921 245 D 156
1511810022741 30 14013.9 82 609 90 47.686167 -117.238893 273 D 156
1511810022991 35 14013.9 82 609 90 47.686167 -117.238861 315 D 156
1511810023241 38 14013.9 82 609 90 47.686168 -117.238822 330 D 156
1511810023491 42 14013.9 82 609 90 47.686168 -117.238778 337 D 156
1511810023741 45 14013.9 82 609 90 47.686168 -117.238728 336 D 156
1511810023991 49 14013.9 82 609 90 47.686168 -117.238674 336 D 156
1511810024241 51 14013.9 82 609 90 47.686168 -117.238614 335 D 156
1511810024491 53 14013.9 82 609 90 47.686168 -117.238544 335 D 156
1511810024741 56 14013.9 82 609 90 47.686168 -117.23847 335 D 156
1511810024991 59 14013.9 82 609 90 47.686168 -117.238391 333 D 156
1511810025241 61 14013.9 82 609 90 47.686168 -117.238309 334 D 156
There are a few more speed clocking recording outputs floating around the
0 to 60 uncork thread as well.