Trimble GeoExplorer 7x

The first time you use the rangefinder on the Geo 7X handheld, you must calibrate the orientation sensors. Maintaining good and current calibration is important to ensure optimal output from orientation sensors and the rangefinder. When correctly calibrated, the orientation sensors report the precise alignment of the planes of the internal GNSS antenna and camera relative to the earth in terms of X, Y and Z axes. During manufacturing, great care is taken to establish a baseline calibration for all components, but due to environmental and use-case factors, each device must occasionally be field calibrated. There are a number of factors that can affect the accuracy and performance of sensors that can be accommodated for with calibration:

Orientation sensors are affected by temperature, and each sensors is unique.
The planet has a varied magnetic field and this affects the performance of magnetic sensors. Using magnetic declination values for a particular area, you can accommodate for coarse variations in magnetic field strength, but by calibrating in your environment, you can achieve greater accuracy.
Local magnetic conditions can affect the device’s own magnetic field.

The Sensor Calibration routine prompts you to calibrate the sensors, and recommends either a fast calibration or a full calibration, depending on location conditions, and the device state. A full calibration may be recommended:

the first time you use the handheld
the first time you use the handheld in particularly hot or cold conditions
when you use the handheld in an area it has not been used in before
after you attach a rangefinder module for the first time
after changing the battery (each battery typically has different magnetic properties).