How can I measure latency when the phone and glasses have different clocks?
Do not subtract device timestamps unless you have established how their clocks align. A common observation clock or a documented synchronization method is needed for a meaningful interval across devices. Local monotonic timing can measure stages on one device without solving cross-device alignment.
Use a shared observation for a simple experiment
A video that captures the starting event and visible result can provide one timeline. Its precision is limited by frame rate and by how clearly those events can be identified. Internal logs can add detail, but they need correlation rather than an assumption that matching-looking timestamps share a clock.
We would keep request identifiers in the logs and state the measurement resolution. For example, a video-based observation should not imply sub-frame precision simply because a spreadsheet can display extra decimal places.