您生成一个报告来显示过去 30 天内用户都来自哪些类型的设备，例如是来自计算机还是手机。在该报告中，下面哪一项是 Google Analytics 中的“指标”？

手机用户数量" (Number of mobile users) is a metric because it is a quantitative measurement, representing the count of users accessing the site via mobile devices. Metrics are numerical values that provide data about user behavior or site performance. "日期范围设置" (Date range setting) is a configuration for the report, not a data point within it. "用户访问您的网站前来自何处" (Where users came from before visiting your website) describes a dimension (source/medium), which categorizes data, rather than a quantifiable value. "设备类型" (Device type) is also a dimension, categorizing users by the type of device they used (e.g., desktop, mobile), not a measurable quantity itself.