Which scenario requires immediate declination of the M2 Aiming Circle?

The scenario that necessitates immediate declination of the M2 Aiming Circle is if it has been dropped. When the M2 Aiming Circle sustains an impact from being dropped, it can affect the internal mechanisms and the calibration of the device. This impact might lead to misalignment, which would compromise the accuracy of any measurements taken. Therefore, re-establishing the correct declination ensures that the aiming circle functions properly, allowing for accurate fire direction and artillery operations.

While other scenarios, such as extreme heat or moving between locations, may influence the operation or require checks to be conducted, they do not inherently necessitate immediate recalibration as dropping the device does. Declination after a set number of uses may be a good practice for maintenance but does not require immediate action in the same way.