HP 8921A Programmer's Manual page 531

RSVD
VMAC
CHAN
Parity
Reserved for future use, all bits must be set as indicated.
8 binary character required.
This field displays the voice mobile attenuation code. It shows the mobile station power
level associated with the designated voice channel.
3 binary character required.
Channel number field. Indicates the designated voice channel.
11 binary character required.
Parity field. The contents of the Parity field cannot be set by the user. The Test Set
calculates the parity bits.
Chapter 8, Programming The Call Processing Subsystem
CALL BIT Screen Message Field Descriptions
531