The observer must be observed, or his observations will misl... - Hipparchus

"The observer must be observed, or his observations will mislead him."

Hipparchus

Astronomer Mathematician Anatolia (Nicaea) 190–120

More from Hipparchus

"The stars are the land-marks of the universe."

"In the celestial sphere, we find the truth of all things."

"Measure twice, cut once; observe twice, conclude once."

"The heavens declare the glory of precision."