the earliest date on which a <#stamp> or item of <#poststa=postal stationery> is known to have been used, as documented by expert opinion.  Generally applied to items issued in the nineteenth and early twentieth centuries that did not have formal <#firstdayofissue=first days of issue> and that might have arrived at different post offices at different times.

the earliest known date on which a stamp is used, even if prior to the official <#firstdayofissue=first day of issue>.  Generally applied to contemporary stamps.

see <#ecom=E-COM>.

1.) a device that employs a beam of light to facilitate more accurate <#perf=perforation> of stamps during the manufacturing process.  2.) the markings (see <#eedash=Electric Eye Dashes>,  <#eemargin=Electric Eye Margin Line>,  <#eegutter=Electric Eye Gutter Bar>, and <#eeframe=Electric Eye Frame Bars>) in the <#margin=margins> and <#gutter=gutters> of sheets of stamps that enable the electric eye device to accomplish its purpose of more accurately perforating stamps.  Stamps with electric eye markings were first sold in 1935.

vertical dashes in the vertical <#gutter> between the right and left <#pane=panes> that were used by the <#eleceye=electric eye> in the <#perf=perforating> process.  First used experimentally in 1933.