The notation combines two distinct tolerance classes from two parts of the standard:
The ISO 2768 standard is a widely adopted international standard that defines the general tolerances for linear and angular dimensions, as well as the geometrical tolerances for machined parts. The standard provides a framework for specifying and verifying the dimensional and geometrical accuracy of parts. iso 2768-mk pdf
Place this in the title block or general notes section of your drawing: The notation combines two distinct tolerance classes from