Refer to figure.
The Artificial Horizon experiences the following errors:
1. Turning errors
2. Acceleration errors
3. Real wander of the gyroscope's spin axis away from its alignment with the earth vertical.

The control system of the air driven artificial horizon depends on the pendulous vanes being affected by the Earth's gravity. However, the vanes will be affected by any acceleration, not just that due to gravity.

• When an aircraft accelerates in a level attitude (e.g. take-off run) a false nose up indication will result. The pitch error is due to the effect of acceleration on the lateral pendulous vanes.
• Deceleration will cause the opposite of the acceleration error indications i.e. a nose down.