What's the difference between whereat and whereto?

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".

Whereto

Definition:

• (adv.) To which; -- used relatively.
• (adv.) To what; to what end; -- used interrogatively.

Example Sentences: