Using accelerometer data and the advanced physics engine from the gMeter app, greenMeter computes power, fuel usage/cost, crude oil consumption, and carbon emission (data can be shown in US or metric units). Thanks to a novel algorithm that computes parameters over the entire speed range, the app does not need GPS, opening usage up to all generations of the iPhone and iPod Touch.
The app offers two calibration options for the accelerometer; one to correct internal offsets, and the other to set the forward direction when the device is positioned in a vehicle (see user manual for suggested positioning).
Settings and preferences, including inputs to specify vehicle, weather, and fuel characteristics, are accessed via the "i" button. The app offers an easy setup mode to help specify vehicle specs.