# Revision history [back]

1. IMU measures angular velocity and linear acceleration. If you integrate the first you can obtain relative orientation not absolute. However, IMUs are typically built with a magnetometer that provide an absolute reference to integrate the relative orientation and get the absolute heading.

2. The IMU driver has to report 0 when facing when facing east (even though its headings increase and decrease correctly). If this does not happen to you, use the yaw_offset parameter from navsat_transform_node. Also, make sure your IMU conforms to REP-105 and check that the signs of your orientation angles increase in the right direction. An IMU that is placed in its neutral right-side-up position on a flat surface will:

• Measure +9.81 meters per second squared for the Z axis.
• If the sensor is rolled +90 degrees (left side up), the acceleration should be +9.81 meters per second squared for the Y axis.
• If the sensor is pitched +90 degrees (front side down), it should read -9.81 meters per second squared for the X axis.
1. IMU measures angular velocity and linear acceleration. If you integrate the first you can obtain relative orientation not absolute. However, IMUs are typically built with a magnetometer that provide an absolute reference to integrate the relative orientation and get the absolute heading.

2. The IMU driver has to report 0 when facing when facing east (even though its headings increase and decrease correctly). If this does not happen to you, use the yaw_offset parameter from navsat_transform_node. Also, make sure your IMU conforms to REP-105 and check that the signs of your orientation angles increase in the right direction. An IMU that is placed in its neutral right-side-up position on a flat surface will:

• Measure +9.81 meters per second squared for the Z axis.
• If the sensor is rolled +90 degrees (left side up), the acceleration should be +9.81 meters per second squared for the Y axis.
• If the sensor is pitched +90 degrees (front side down), it should read -9.81 meters per second squared for the X axis.