At some point of time Precision and Extra Precision grades were built in house. But not before the precision factory was opened. Gruen did not have their own factory at that time! They left their customers under the impression that they had that, but this is not true.
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The first years of the the Precision Factory it is said that only pocket watch movements have been built there. It took Gruen more than 10 years to move also other products to their own factory.