What's the difference between where and whereat?

Where

Definition:

• (pron. & conj.) Whether.
• (adv.) At or in what place; hence, in what situation, position, or circumstances; -- used interrogatively.
• (adv.) At or in which place; at the place in which; hence, in the case or instance in which; -- used relatively.
• (adv.) To what or which place; hence, to what goal, result, or issue; whither; -- used interrogatively and relatively; as, where are you going?
• (conj.) Whereas.
• (n.) Place; situation.

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".