The Acaia scales are designed with a lab-balance-grade level performance. The higher the resolution is, the more frequent you need to calibrate the scale.
For example, a scale that weighs from 0.001 g (1 mg) in the lab is required to be calibrated "each time" you weigh an object.
For Acaia scales, we have a high resolution that we would recommend a daily calibration for commercial use (cafes). If you're a home user, every month will work. And if you take the scale on your travel adventures, you should calibrate at the new location.