> For the complete documentation index, see [llms.txt](https://carec.gitbook.io/carec-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://carec.gitbook.io/carec-docs/documentation/reference/units-frames-and-time.md). # Units, Frames, and Time ## Units Use SI units unless an interface explicitly requires otherwise: * Distance: meters * Linear velocity: meters per second * Angular velocity: radians per second * Acceleration: meters per second squared * Angle: radians internally; degrees only for user-facing output * Time: seconds with explicit resolution * Temperature: degrees Celsius * Voltage/current: volts and amperes ## Coordinate frames Define a stable base frame, odometry frame, map frame, sensor frames, and drive/control frames. Document axis direction, origin, mounting transform, calibration version, and allowed update source. ## Time Specify clock source, monotonic versus wall time, synchronization, timestamp at capture, maximum age, and behavior after clock reset. Measurements include validity, uncertainty or covariance, and health where they affect safety or autonomy. --- # Agent Instructions This documentation is published with GitBook. GitBook is the documentation platform designed so that both humans and AI agents can read, navigate, and reason over technical content effectively. Learn more at gitbook.com. ## Querying This Documentation If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question. Perform an HTTP GET request on the current page URL with the `ask` query parameter, and the optional `goal` query parameter: ``` GET https://carec.gitbook.io/carec-docs/documentation/reference/units-frames-and-time.md?ask=&goal= ``` `ask` is the immediate question: it should be specific, self-contained, and written in natural language. `goal` is optional and describes the broader end goal you are ultimately trying to accomplish on behalf of the user. GitBook uses it to tailor the answer towards what is most useful for that goal. The response will contain a direct answer to the question and relevant excerpts and sources from the documentation. Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.