Phyiscal method validations - Specific Gravity/Particle size etc


Quick query - a standard physical method would be classed under the ICH guidelines as a performance characteristic Category III, and as such requires an assessment of precision.

What would be the best way to validate physical methods? same approach as chemical i.e. x2 days with 2 analyst and 6 replicates? or should we perform GR&R studies as say for example a hydrometer could be considered a gage? and is GR&R what acceptance limits can/should be applied.

Any thoughts