As detailed above, an independent claim should specify explicitly all of the essential features needed to define the invention. This applies except insofar as such features are implied by the generic terms used, e.g. a claim to a "bicycle" does not need to mention the presence of wheels.
In the case of a product claim, if the product is of a well-known kind and the invention lies in modifying it in certain respects, it is sufficient that the claim clearly identifies the product and specifies what is modified and in what way. Similar considerations apply to claims for an apparatus.