Which of the following is not a measurable result of using a customer service application?

The option that indicates that customer service will use the app to record maintenance is not a measurable result of using a customer service application. This statement describes an intended action or a feature of the application rather than an outcome or performance metric. While it suggests that the application will facilitate data entry by the service team, it does not provide any quantifiable results or improvements related to customer service performance.

In contrast, the other choices reflect specific, quantifiable outcomes that can be assessed to measure the effectiveness of the application. For example, decreased support calls by a certain percentage reflects a tangible reduction in demand for assistance, which can be linked to improved customer satisfaction or efficiencies gained through the application. Similarly, a decrease in average call duration quantitatively indicates a faster resolution process, which is often a key performance indicator in customer service scenarios. Lastly, having every registered vehicle with an up-to-date maintenance history is an outcome that reflects improved data management and customer service capability, providing a measurable way to assess the application's impact on operational efficiency.

Thus, the first choice fails to present a measurable result, making it the correct identification.