ssn-system:Precision not used in TS

ssn-system:Precision is not mentioned in TS v2.1.1. There is s4ehaw:precision and ssn-system:Precision, which adds confusion and in the W3C Spatiotemporal Data on the Web working group, there are discussions concerning potential deletion of the ssn-system module.

so my suggestion is to simply define an instance of saref:Property instead.