Product Specification 11.Three items stapled together.The first is a letter from The British Electrical and Allied Manufacturers Association dated 21/6/1949. The second is a printed 20 page document from the Radio Components Standardisation Committee titled 'D-RCS 231, Specification for Electrical Indicating Instruments Hermetically Sealed, 1st Draft Issue 1' dated January 1949. The third is a two page typed amendment to D-RCS 231.