The graph expresses the annual evolution of the frequency of use of the phrase «pocketknife» during the previous 500 years. On a pocketknife, it's good to have the stainless selection, which is easy to take care of.
The blade holder might either retract or fold into the handle, very similar to a folding-blade pocketknife. The truth is, the old school pocketknife is still among the many best promoting knifes of all time.