Best and most accurate way to track miles in a 2012 Tesla Model S

[radiantMemory]

Hi there, I was wondering on the best and most accurate way of tracking business miles in a Tesla Model S?
I thought about using apps like MileIQ or Everlance, but they can be pretty inaccurate capturing like 85-95% of total miles. Thought about using a physical device like The Mileage Ace which has about 99% accuracy.
And maybe even a device that connects to the car via the OBD-II reader (but I've heard that Tesla disabled data readings or whatever due to security reasons).
But with the car being so advanced, is there a way to track miles using Tesla's API (if they have any) like using an app like Teslab

.
Taking accurate logs is important since I will be using the vehicle for business use most of the time, and will definitely be useful for saving big money come tax time.

Sorry if my question is all over the place lol

Thanks~

 

[Lasttoy]

Teslafi tracks

 

[HankLloydRight]

Yes Teslafi.com is the best tool for this.

Also, the OBDII port is not just disabled, it's neutered... It only offers pins for +12v power. There's a proprietary diag port instead.