minor variations between apparently identical <#stamp=stamps> that were printed from different <#plate=plates>. Plate varieties can result from a damaged plate, or when there is some irregularity in the way a plate is made. Plate varieties are <#constvar=constant>, that is, as long as the variety appears on the plate, it will appear on every <#sheet> produced from that plate. More information about Plate Varieties may be obtained by referring to the Encyclopedia of Plate Varieties on U.S. Bureau-Printed Postage Stamps.