it is used to calibrate the sound level meters

The sound level meters has two models of ND9A, ND9B.  
It fits for the standards of GB/T15173, ANSIS1.40 CLASS2, IEC942.
the frequency is 1000Hz.
The power supply is 1*9v 6f22 battery.
the dimension is 142*47*47mm.
The weight is 275g which not includes the battery.

The standard delivery includes:  main unit 1; carrying case type  1; instruction manual  1