TDMS: What is the difference between "NI_UnitDescription" and "unit_string"?

[JKSH]

When we wire analog waveforms from DAQmx Read into TDMS Write, the channel automatically gets a property, "NI_UnitDescription".

However, https://zone.ni.com/reference/en-XX/help/371361R-01/glang/tdms_set_properties/ only mentions the property "unit_string", not "NI_UnitDescription".

What is the difference between these two properties? Which one should we use when manually writing units into TDMS files?

• If I manually write "unit_string", then DAQmx channels will get 2 copies of units
• I can't tell if there are any downsides to manually setting "NI_UnitDescription"