A retentive timer has which characteristic?

A retentive timer is designed to maintain its current accumulated time even when there is an interruption in the input signal or power supply. This characteristic makes it particularly useful in applications where it is essential to track time over periods of inactivity. For example, if a machine pauses for any reason, the timer will retain the time it recorded up to that point, allowing operations to resume seamlessly when the input is restored.

The other options do not accurately describe the functionality of a retentive timer. For instance, the inability to maintain accumulated time or requiring continuous power would disqualify it from being classified as a retentive timer, as it is inherently designed to be resilient against interruptions. Similarly, resetting immediately upon interruption contradicts its fundamental function of retaining the time count. Thus, the correct understanding of a retentive timer hinges on its ability to continue counting time through interruptions, solidifying its role in various control systems.