What's the difference between thereagainst and whereat?

Thereagainst

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Definition:

Example Sentences:

Whereat

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Definition:

• (adv.) At which; upon which; whereupon; -- used relatively.
• (adv.) At what; -- used interrogatively; as, whereat are you offended?

Example Sentences:

• (1) ), whereat measurements can be taken either using cylindrical graphitic walls or "no walls".