Accelerometers are sensitive to gravitational force, allowing them to be used to determine the attitude of the sensor with respect to the reference gravitational vector. This attitude determination is very useful for detecting tilt or rotation for screen rotation of handheld devices. Based on the orientation of the device, images and text can be rotated on the screen to appear upright to the user. For example, with device orientation if a mobile phone is sitting flat on a desk and an incoming call is received, flipping the phone over can direct the call to voicemail. When the device is right side up, the Z-axis acceleration is close to 1g. When the device is upside down, the Z-axis acceleration is close to –1g.