Each Gemtrac unit comes with a left and right bank of drawers, these get divided into two groups of Zones. In this example we will use Red and Green colors to identify the Zones correctly.

Focusing on the red bank, each drawer is identified as a Zone. First drawer would be Red-1, second drawer Red-2 etc. Start at the end opposing to where you will put any expansion Gemtracs to ensure the new additions are in successive numerical order.