You can use many instruments to measure length.You can use a scale.There are devices which are laser guided and can be used to do that same.Satellites are also used for measuring the length for the large distances.You can use a meter scale.You can also use the inch tapes those have a strip of fiber with measurements printed on them.
There are so many tools for finding the length .These are screw gauge,ruler,measuring scale ,cicular scale.
measuring tape
You can use anything to find what you are looking for.
common tools scientist use to measure length mass and liquid volumes are as follows. for length tools are rulers,vernier calipers ,circular scale ,etc . for mass tools are beam balances . for volume tools are beaker ,flask,pipette,etc.
The longest length would be the hypotenuse. You can use SOHCAHTOA to find the length.
It is necessary because measuring tools help you measure the length of an object accurately.
Millimetres
a millimeter
centimeters
Centimetre
Roget's Thesaurus Roget's Thesaurus
Metres.
Micron