Which of the following is NOT reliable for accurate measurement of length? 

• Our senses are not reliable for accurate measurement because they merely estimate the measurement and do not give the actual measurement. 
• For example, while measuring the length of a table we may estimate it to be 1 metre using our senses but the actual length of the table can be less than or more than 1 metre.
• Also, the estimation of measurement may vary from person to person if they rely only on their senses.
• Whereas, regardless of who takes the reading, a measuring tape, metre rod, or ruler will always provide the exact same measurement.

Therefore, 'Our senses' is the correct response.