During the CFT, what is required to ensure the ammo can weighs accurately?

The accurate measurement of the ammo can's weight during the Combat Fitness Test is crucial for ensuring that the test is conducted under consistent and standardized conditions. A calibrated scale is essential because it has been adjusted to provide precise measurements. This calibration ensures that the weight of the ammo can is correct, which directly impacts the evaluation of the performance of the Marines participating in the test. Using a calibrated scale eliminates discrepancies that could arise from using an uncalibrated device, thereby maintaining the integrity of the testing process and helping to ensure that all participants are assessed fairly.

The other options, while potentially useful in various contexts, do not serve the specific purpose of accurately measuring weight. For instance, a standard ruler measures length rather than weight, a weighing bag would not provide a measurement without a scale, and a manual counter does not measure weight at all. Therefore, the necessity of using a calibrated scale becomes evident in guaranteeing that the weight measurement is both accurate and reliable.