At1-9(1)

In many city codes, this refers to a specific type of "Apartment" or "Residential" zoning sub-district (often regarding density or height limits).

It might refer to a specific clause in an aviation, mechanical, or electrical manual. AT1-9(1)

To provide a helpful essay, I need a little more context on what refers to. This code typically pops up in a few very different fields: In many city codes, this refers to a