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Try closing all instances and windows of the Quark program.
Then go to the Preferences folder for the Quark program (located variously according to the Quark version) and select, then delete, a specific file
and then you can try Quark again. See if that gets the Measurements palette back.
If it does not work, then let me know.
(I presume you have already tried:
Ctrl-click on the Measurements palette title bar, and select
Always Show Tab Bar.)