An OccurrenceRecord may represent more that just the presence of an instance of a taxon in the wild. If the occurrence is the result of a survey there may well be a quantitative measure associated with the record such as a count or frequency. In the most simple case this property may contain the integer 0 indicating a lack of occurrence. If this property is present then its meaning (including units) should be interpreted in terms of the value of the procedure property. The associated valueConfidence property is provided to hold indication of error or deviation - again dependent on the procedure followed.