VSS standard catalog uses the units defined in this file. They are also described in the VSS documentation.
It is possible to replace the default units by the --units/-u parameter, see vspec documentation.
The syntax of the file with units shall follow this pattern:
puncheon:
definition: Volume measure in puncheons (1 puncheon = 318 liters)
unit: Puncheon
quantity: volume
allowed_datatypes: ['uint16', 'int16']
hogshead:
definition: Volume measure in hogsheads (1 hogshead = 238 liters)
unit: Hogshead
quantity: volume
allowed_datatypes: ['numeric']