macOS provides two commands to pull storage information: df -h and du -sh ~. These commands use the df and du utilities, which display free disk space and disk usage information. The values they return can be close to the data seen via the device's GUI, but it will not be the same; further unknown calculations are run on the device to get that number. Apple does not disclose this data.
If the value returned via Addigy and commands differs significantly from the information provided in the GUI (i.e., Finder), this may be due to purgeable space on the device. There is no known way to pull this information on purgeable space via commands.