What must be included in a Message to Observer?

The correct answer highlights that a Message to Observer must include changes to the call for fire. This is essential because any modifications in the initial call for fire directly impact the execution of the fire mission. The observer must clearly communicate these changes to ensure that the intended target is engaged effectively and accurately.

Including alterations to the call for fire helps in maintaining clarity in communication and ensures that all parties involved have the most current and correct information, reducing the risk of miscommunication or operational errors.

While weather conditions and enemy positions are certainly relevant in a broader operational context, they are not the primary focus of a Message to Observer. The primary goal of this message is to ensure that changes relevant to the fire support coordination are conveyed, making the information about the call for fire critical and central to the communication process.