Question

What is parallax error?

Answer 1

Assuming you want to find the length of something, so you use a ruler. To read the measurement, you have to read it directly above to get the real reading. By tilting your head abit, the measurement will be off because of perception. This is known as parallax error. Instead of getting, maybe 10cm, you get 9cm or 11cm, depending on where you tilt your head and/or where the ruler starts.