Custom / Own efficiency rate

Hi TeslaFi Team
It would be great if, instead of the automatic efficiency judgement, we could create our own value, e.g. 230 Wh / km.
Of course sometimes, i have with round about 200 Wh/km 105% efficiency rate, and sometimes with the same conpsumtion (200 again) only 84%. (same car, Model X P100D)
 Would that be a big effort?
Thank you & greetings from Switzerland (and sorry for my english)
Miklos