It’s a proof certificate from the Spanish proof house in Eibar. Looks to be for a 20 gauge, 70cm chambers, it was dated 1964. The serial number of the gun was 192558. It passed standard proof for 2 3/4” chambers. The barrels are (were, sometimes bad things happen) 71.2cm long, just a bit longer than 28”. It was a SXS double, measurements are indicated for both of them.

Best,
Ted