What form would an observer use to keep track of the rounds and spottings in relation to the registration point?

The choice of DA 5429 as the form used by an observer to keep track of the rounds and spottings in relation to the registration point is accurate due to the specific purpose of this form. DA 5429, also known as the "Fire Support Request," is specifically designed to document fire support requests and observations. It allows observers to record the essential details about each round fired, including the target, adjustments made, and the effects observed. This is critical for maintaining accurate records and ensuring effective follow-up on target adjustments based on prior rounds.

In contrast, DA 4187 is a form utilized for personnel actions and does not pertain to fire support operations. DA 2185 is a form for submitting requests for ordnance and is not focused on tracking rounds or spottings. The Shell Report, while related to artillery operations, does not serve as a dedicated format for an observer to systematically record rounds and spottings in relation to a registration point. Thus, DA 5429 is the most relevant and functional form for observers engaged in tracking this specific type of information in military operations.