Roundrobin auto-assignment of Users for different offices

I am trying to perform a round robin assignment, for different techs in our different offices.

My Atlanta office has 3 techs (tech1, tech2, tech3) "ATL"

My Chicago office has 3 techs (tech4, tech5, and tech6) "CHI"

So if a issue is created for Office "ATL", I'd like to pass each one to the next tech in line.

first issue: tech1
second issue: tech 2
third issue: tech 3
fourth issue: tech 1
etc.

I had tried to use the example from:
http://www.quickbase.com/developer/knowledge-base/how-can-i-auto-assign-records-users-my-application...


If(
Mod([Record ID#],ToNumber([number_of_reps])) = 0, ToUser("user_screen_name_or_email"),
Mod([Record ID#],ToNumber([number_of_reps])) = 1, ToUser("user_screen_name_or_email "),
Mod([Record ID#],ToNumber([number_of_reps])) = 2, ToUser("user_screen_name_or_email "))

But I'm not sure how to setup using the Office selection: [Office] = "ATL" or [Office] = "CHI" in the current list.

So I'm trying to do something like:

If(
Mod([Office]= "ATL", Mod([Record ID#],ToNumber([ATL_techs])) = 0, ToUser("tech1"),
Mod([Office]= "ATL", Mod([Record ID#],ToNumber([ATL_techs])) = 1, ToUser("tech2"),
Mod([Office]= "ATL", Mod([Record ID#],ToNumber([ATL_techs])) = 2, ToUser("tech3"),
Mod([Office]= "CHI", Mod([Record ID#],ToNumber([CHI_techs])) = 0, ToUser("tech4"),
Mod([Office]= "CHI", Mod([Record ID#],ToNumber([CHI_techs])) = 1, ToUser("tech5"),
Mod([Office]= "CHI", Mod([Record ID#],ToNumber([CHI_techs])) = 2, ToUser("tech6"),
)


But that hasn't worked for me.

Any suggestions?

Thanks,
Tom