It's the mother of all sound meters.
All the other instruments had valves.
Produced for 21 years, it sold a record number of 17300 units.
The build quality is superb !!! & I love the Danish design.
I own two. It's big, heavy & built like a tank. Still working after 50 years.
Below is a later model : The 2209 (peak detector) in it's lovely padded case.
The manual describes it as " a compact & portable instrument for precision sound & vibration measurements".