Going Under

This was the first time I had ever seen floors with negative numbers.

Elevator Negative Floors

I wonder why they opted for this naming system instead of B1 and B2 (for basement one and basement 2) or some other scheme.

I do not think I would understand if someone told me:

“Come on by my office. I’m on the negative second floor.”

Do you have any ideas for a better way to name subterranean floors?