1. A product unit specific indicator operative to provide a machine-readable indication of exceedence of at least one acceleration threshold, said indicator comprising: a mechanical indicator having a first operative orientation prior to exceedance of said at least one acceleration threshold and having a second operative orientation following exceedance of said at least one acceleration threshold; at least a first part of said mechanical indicator being readable as part of a bar code when said mechanical indicator is in said first operative orientation, and at least a second part of said mechanical indicator being readable as part of a bar code when said mechanical indicator is in said second operative orientation.