1. A system comprising: an image sensor configured to produce a first signal that represents an image that includes a feature of a user; an orientation sensor configured to produce a second signal that indicates an orientation of the image sensor with respect to a gravitational force exerted by the Earth; a processor configured to: generate angle measurement of the feature of the user based, at least in part, on the first signal; generate a comparison between the angle measurement and metric measurements; and based on the comparison, generate an output indicating how an orientation of the user compares with the metric-measurements.