What's the difference between hereunto and whereat?

Hereunto

Definition:

• (adv.) Unto this; up to this time; hereto.

Example Sentences:

• (1) In token whereof I have hereunto set my hand this tenth day of December, 1936, in the presence of the witnesses whose signatures are subscribed.

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".