Spicer Airmatic 4 spd

Looking at a truck with an 18spd and a spicer 4 spd. aux trans. Can anyone tell me how you would shift this? It does not have 2 sticks it has a small stick next to the drivers seat, with splitters on it but the stick itself does not move.

 

By splitters I mean it is an air shift aux tranny

 

Here is the pic of what it looks like. Was wondering if you could use this in all the gears or if it just something you would use in the big hole to split it four more times.

 

Sounds like what I was thinking, thankyou. I was hoping that that is how it would operate