When using a pressure-sensor altimeter in a rocket that won't reach Mach 1, what must be done?

When utilizing a pressure-sensor altimeter in a rocket that will not reach Mach 1, it is essential to ensure that the altimeter has access to atmospheric pressure changes in order to function accurately. By drilling one or more holes to allow for atmospheric access, the altimeter can respond to changes in air pressure as the rocket ascends and descends. These holes permit the altimeter to sense the surrounding atmospheric conditions, which are critical for the altimeter to measure altitude correctly based on pressure differentials.

Without appropriate atmospheric access, the altimeter may provide inaccurate or erroneous readings since it relies on the change in air pressure to calculate altitude. Therefore, modifying the rocket to allow pressure changes to reach the altimeter is a necessary step to ensure its proper operation and reliable data.

In contrast, simply not making modifications or using a different type of altimeter could lead to incorrect altitude readings or the loss of the altimeter's functionality entirely in scenarios where pressure data is vital for altitude determination.