What does a ref use?

Excuse me, could you clarify what a ref typically utilizes in their line of work? Are they referring to specific tools, equipment, or perhaps a set of guidelines or rules that they adhere to? I'm curious to understand the context in which this question is being posed, as the term 'ref' can have multiple meanings depending on the industry or activity being discussed. If we're talking about sports, for instance, a referee might use whistles, flags, and a set of rules to govern the game. However, if we're discussing a different field, the answer could vary significantly. Could you please provide some additional context or clarification?