The origin of Van Maanen's measurement errors where that Van Maanen used a stereo blink comparator comparing new plates with plates some 10--20 years old, and by blinking between those two plates he could detect small discrepancies on the positions of the objects.
The origin of van Maanen's measurement errors emerged from his stereo blink comparator, which van Maanaan used to compare new plates with plates some 10--20 years old. By blinking between those two plates he could detect small discrepancies on the positions of the objects.