What does full deflection of a survey meter while on battery check indicate?

When a survey meter shows full deflection during a battery check, this indicates that the meter is receiving power and functioning to some extent, but does not guarantee that it is measuring radiation accurately. Full deflection suggests that the needle moves to the maximum position, which means that the circuit is closed and that the meter is working at least in terms of electrical functionality. However, it does not confirm that the meter is properly calibrated or that it will function correctly when measuring radiation levels.

The readings could be inaccurate due to various factors, such as the need for recalibration or other technical issues that may not affect its ability to display signal power but do affect its effectiveness in radiation detection. Therefore, while full deflection denotes that the device is operational in terms of power, it leaves open the possibility that other performance issues may exist that affect accuracy.