BUG
Attempts to switch to Decimal Degrees, after setting the display units to Degrees Minutes Seconds on the General tab of the Data Frame Properties dialog box, fail. However, this issue does not occur if the data frame display units are modified on the Data View tab of the ArcMap Options dialog box.
The cause of this bug is unknown, but the issue can be avoided by specifying the data frame display units on the Data View tab of the ArcMap Options dialog box.
If the display units on the General tab of the Data Frame Properties dialog box have been changed to Degrees Minutes Seconds, and it is necessary to switch to Decimal Degrees, use the following workaround.
Note: A coordinate system must be assigned to the data frame on the Coordinate System tab of the Data Frame Properties window before the display units can be changed.
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