Est 1970's, I suspect it was intended for sizing users to the PGM as most of the other masks Bulgaria used were open backed so it wouldn't make much sense to use a sizing tool versus the PGM is a full head pull over mask so sizing before trying on may have been a ideal system. Comes from a Smoke Free and Pet-Free home. Shipping/Payments: Payment is expected within 3 days of auction/listing end. Combined shipping is avaliable, requests for combined shipping on 'free shipping' items may sometimes result in the price of the item to be lowered if applicable. International Shipping: It's your responsibility to know your custom laws, I am not responsible for additional custom fees, violation of importation laws and/or most other problems that may occur at (non-US) customs.