Signed Brüel & Kjaer, made in Denmark, Pistonphone type 4220 with a 124 dB head, serial 347444. High quality sound level calibration instrument from the 1960's for professionals. Clean battery compartment, 6X standard AA batteries required (not included). Original, clean inside out, light wear only, easy to disassemble. Unit is functional but calibration and servicing may be required due to age. From the estate of a private collector in Montreal (Quebec, Canada).