DUT versus UST

After a wonderful weekend in the Swiss alps climbing the

Diechterhorn, here is a
follow-up explanation by Jeremy Sawicki of Autodesk on the difference between DisplayUnitType and UnitSymbolType
in continuation of our last discussion on the

unit suffix.

Question: What is the exact difference between DisplayUnitType and UnitSymbolType, please?

For instance, the default project unit settings on my system for a length are DUT_Millimetres and UST_None … I wonder what exactly that means?

Also, can you suggest a way to obtain the display string representation shown in the user interface for either of these?

Answer: The simplest answer is based on the UI.
In the Format dialog box, DisplayUnitType corresponds to the Units dropdown:

And UnitSymbolType corresponds to the Unit symbol dropdown:

In most cases, the DisplayUnitType determines the actual unit, for example feet vs. meters, with a different conversion factor applying to each DisplayUnitType. UnitSymbolType affects how the units are indicated on the screen, usually with a suffix. For example, square feet can use a suffix of either SF or ft² or no suffix at all. UnitSymbolType used to be called UnitSuffixType until we introduced a currency unit type, which uses prefixes in some cases, like $.

The above applies to most normal units which are displayed as a number followed by a suffix, but there are various special cases. For example, DisplayUnitType is also used to select certain kinds of units with special formatting, like Feet and fractional inches or Degrees minutes seconds.

I don’t believe there is currently any API that can get the names of display unit types or unit symbol types.

Many thanks to Jeremy for this helpful clarification!