It currently seems impossible to convey two-dimensional data with a domain unit other than time as the value of an observation. The SampledData datatype includes a period whose description requires milliseconds as the unit of distance between samples. There are, however, use cases that require a different domain unit. Consider, for example, frequency resolution for EEG. As discussed in the Healthcare Devices (DEV) group, we would like to see the specification modified in order to facilitate other domain units.

There may be more than one option to achieve this, but this solution appears to be the simplest: Change the description of SampledData.period to something like "distance between samples"; add SampledData.domainUnit 0..1 CodeableConcept (which could default to milliseconds if no value is given); and update the surrounding descriptions that currently mention time as the domain unit.