On the top right side of the screen there is a gear for settings. Click it. It will take you to the "Manage Account" screen with 5 buttons to chose from, choose the one in the middle: "App Settings" Click it. You are then presented with a page that displays your Hub Works apps, Select "Zip Schedules." Click it. The next screen will display 3 buttons with the first one being "Positions." Click it. There you have it... You may now add more positions.
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Took me 30 minutes to find it the first time and this time about the same. This should be an easy thing to find and I don't get why they keep moving it around in the background... Put it on the main schedule display page next to the "+Add Employee" button. There is plenty of room, and it should be quick to access, not hidden.