What's the difference between thereunto and whereat?

Thereunto

Definition:

• (adv.) Unto that or this; thereto; besides.

Example Sentences:

Whereat

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".