What's the difference between thereagainst and whereon?

Thereagainst

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Definition:

Example Sentences:

Whereon

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Definition:

• (adv.) On which; -- used relatively; as, the earth whereon we live.
• (adv.) On what; -- used interrogatively; as, whereon do we stand?

Example Sentences:

• (1) With the patient in a supine position, the droplets could be positioned over the macula in the preretinal vitreous space, whereon the FTBA PO2 could be influenced by the preretinal oxygen concentration.
• (2) The heart was the only one of all the internal organs whereon significant pathologic changes were observed during autopsy.