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You can disable a memory for pretranslation by unticking the Pretranslation use option. In that case the memory is not used by the Beebox.
If the memory contains a lot of terms you may want to tick Alignment dictionary. Whenever, the system aligns content it will use your memory content to enhance alignment quality. This only makes sense if your memory mostly contains words or terms. Do not tick if your memory is made up of sentences and phrases. It is generally better to upload dedicated alignment dictionaries.
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Also see Alignment Dictionaries.