UIAccelleration value range

Question

The AppleDeveloper guide seem to imply that UIAccelerationValue can range between a double value of -1.0 and +1.0.

I have logged the values from a real device whilst "shaking" with crazy gestures my iPod touch and got x values above 2.0 (e.g. +2.1, -2.1) and NO y value above 2.0f.

• Could anyone explain this?
• Has anyone identified the MAX and MIN values for UIAccelerationValue?

My take on this is that Apple has implemented some algorithm that approximates the force of gravity and takes as 1.0 values that are above a standard speed approximation (e.g. have values 9.8 m/s of speed).

• Any other guesses?

Answer 1

You may be misunderstanding a part of the documentation. Nowhere does it say that the value ranges between -1.0. and 1.0, as far as I can see. It says that:

The device accelerometer reports values for each axis in units of g-force, where a value of 1.0 represents acceleration of about +1 g along a given axis. When a device is laying still with its back on a horizontal surface, each acceleration event has approximately the following values:

"g" is used in a particular technical sense here; 1 g is one standard gravity; a phone accelerating faster than this will register readings higher than 1. Violent shaking in the hand is easily enough to cause acceleration and deceleration values higher than 9.8m/s².