How do we find the error in single measurement?

Question

unklerhaukus · Answer

what scale were you using

anonymous · Answer

Let's say i'm using a 30 ruler with smallest scale of mm?

anonymous · Answer

You probably mean the precision, since you can't possible know the error.  The precision is usually one digit past the last marked dvision, if you have an analog instrument.  So for a ruler marked in mm, you would report your measurement to the nearest 0.1 mm, estimating the final digit.

For digital instruments, you would typically simply read off the display, and assume the manufacturers knew what they were doing.

anonymous · Answer

I watch prof. Lewin's class in mechanics. I saw him deciding error just with one measurement.

anonymous · Answer

No you didn't.  I understand that's what you think you did, or perhaps even what he said he did, in which case you're both wrong.