During the ETD installation, what is the maximum allowable difference in psi when comparing ETD display and HTD reading?

The maximum allowable difference of 3 psi between the ETD (Electronic Train Device) display and the HTD (Hand Held Tool Device) reading is established to ensure that accurate and timely information is available for the operation of the train. This tolerance allows for minor discrepancies that might occur during the measurement process due to calibration differences, gauge accuracy, or changes in pressure that may occur while readings are taken.

Maintaining this 3 psi limit is critical because it ensures that both devices are still in agreement to a reasonable margin, validating the reliability of the brake system's pressure readings. If the difference were greater than this limit, it could indicate a larger issue with the air brake system or the measurement devices, potentially leading to unsafe conditions during operation. Thus, this limit serves as a safeguard for maintaining operational integrity while allowing for some practical variability in the measurements.