A pipe is measured once with a steel tape with markings every .1mm.The two ends of the pipe line up with the 0 and 40-m marks onthe tape. How should this datum be recorded using theappropriate number of significant figures?

Question

A pipe is measured once with a steel tape with markings every .1mm.The two ends of the pipe line up with the 0  and 40-m marks onthe tape.  How should this datum be recorded using theappropriate number of significant figures?

anonymous · Answer

well bet cause the smallest division is .1mm you would divide that by 2 so you would get + or - .05mm so I'm almost positive it should be to 40.00 and 0.00

mathmate · Answer

That is correct, i.e. 40$\pm$ 0.00005 m, assuming the operator has excellent eye-sight.

Do note that a temperature deviation of 1 degree changes by about 0.00044 m over the 40m. length.

Also, all tapes have rated tensions when measuring.  Any deviation of 1 kg force on the tension can lead easily to an error of 0.00050m over the 40 m. length. (if tape is made of steel.  If it is nylon, the error is MUCH higher).

Therefore the given measurement has to be taken under extremely controlled conditions to get the calculated accuracy.  ALternatively, environmental errors have to be corrected.  They are 10-100 times greater than the graduation error.