What do the A/B values represent on the bottom left of the Global screen?

[mono.mu]

Hi, sorry if this a noob question but I couldn't find anything in the manual. Just out of curiosity - on the Global screen I can see the OS version on the bottom right, and on the bottom left there are 2 values (ie A3 B7) which change when a key is played. What do these represent? Are these which voice is being played (0-7) and which layer (A/B)?