Instances of the class [[Observation]] are used to specify observations about an entity at a particular time. The principal properties of an [[Observation]] are [[observationAbout]], [[measuredProperty]], [[statType]], [[value] and [[observationDate]] and [[measuredProperty]]. Some but not all Observations represent a [[QuantitativeValue]]. Quantitative observations can be about a [[StatisticalVariable]], which is an abstract specification about which we can make observations that are grounded at a particular location and time. Observations can also encode a subset of simple RDF-like statements (its observationAbout, a StatisticalVariable, defining the measuredPoperty; its observationAbout property indicating the entity the statement is about, and [[value]] ) In the context of a quantitative knowledge graph, typical properties could include [[measuredProperty]], [[observationAbout]], [[observationDate]], [[value]], [[unitCode]], [[unitText]], [[measurementMethod]].