Can they use my breath test if the machine wasn't calibrated?

The premise needs adjusting first. People imagine a single calibration certificate that either exists or doesn't. What actually exists is a maintenance history: monthly agency inspections, annual department inspections, and additional inspections whenever an instrument comes out of or goes back into evidentiary use.

Florida's standard is substantial compliance. Insubstantial differences between the approved procedure and what actually happened won't invalidate a result, which is why "the machine was off by a hair" arguments usually go nowhere.

But the State carries the burden of showing that substantial compliance. Where a required monthly inspection is missing entirely, where an instrument was used during a gap in the record, or where repairs were performed by someone not authorized to perform them, courts have excluded the results.

The difference between those two categories — a technicality and a genuine failure — is the whole analysis.