CODE EXAMPLE FOR CSHARP

DisplayUnitType revit api

//Pre 2021
                        DisplayUnitType displayUnitType = fp.DisplayUnitType;
                        value = UnitUtils.ConvertFromInternalUnits(nullable.Value, displayUnitType).ToString();
                        //2021
                        ForgeTypeId forgeTypeId = fp.GetUnitTypeId();
                        value = UnitUtils.ConvertFromInternalUnits(nullable.Value, forgeTypeId).ToString();